- What's New
- Function Overview
-
Service Overview
- ELB Infographics
- What Is ELB?
- ELB Advantages
- How ELB Works
- Application Scenarios
- Differences Between Dedicated and Shared Load Balancers
- Load Balancing on a Public or Private Network
- Network Traffic Paths
- Specifications of Dedicated Load Balancers
- Notes and Constraints
- Security
- Permissions
- Product Concepts
- ELB and Other Services
-
Billing
- Billing Overview
- Billing Mode
- Billing Items (Dedicated Load Balancers)
- Billing Items (Shared Load Balancers)
- Billing Examples
- Bills
- Arrears
- Stopping Billing
- Cost Management
-
FAQs
- When Do I Need Public Bandwidth for ELB?
- Will I Be Billed for Both the Bandwidth Used by the Load Balancer and the Bandwidth Used by Backend Servers?
- Do I Need to Adjust the Bandwidth of Shared Load Balancers Based on the Bandwidth Used by Backend Servers?
- Can I Modify the Bandwidth of a Load Balancer?
- What Functions Will Become Unavailable If a Load Balancer Is Frozen?
- Getting Started
-
User Guide
-
User Guide for Dedicated Load Balancers
- Using a Dedicated Load Balancer
- Permissions Management
-
Load Balancer
- Dedicated Load Balancer Overview
- Creating a Dedicated Load Balancer
- Enabling or Disabling Modification Protection for Dedicated Load Balancers
- Modifying the Basic Configurations of a Dedicated Load Balancer
- Modifying the Network Configurations of a Dedicated Load Balancer
- Exporting Dedicated Load Balancers
- Deleting a Dedicated Load Balancer
- Copying a Dedicated Load Balancer
- Enabling or Disabling a Load Balancer
- Listener
- Backend Server Group
- Backend Server
- Health Check
- Security
- Access Logging
- Tags and Quotas
- Cloud Eye Monitoring
- Auditing
-
User Guide for Shared Load Balancers
- Permissions Management
-
Load Balancer
- Shared Load Balancer Overview
- Creating a Shared Load Balancer
- Configuring Modification Protection for Shared Load Balancers
- Changing the Network Configurations of a Shared Load Balancer
- Deleting a Shared Load Balancer
- Enabling or Disabling a Shared Load Balancer
- Enabling Guaranteed Performance for a Shared Load Balancer
- Listener
- Backend Server Group
- Backend Server
- Health Check
- Security
- Access Logging
- Tags and Quotas
- Cloud Eye Monitoring
- Auditing
- Self-service Troubleshooting
- Appendix
-
User Guide for Dedicated Load Balancers
-
Best Practices
- Using IP as a Backend to Route Traffic Across Backend Servers
- Using Advanced Forwarding for Application Iteration
- Integrating WAF with ELB to Protect Your Websites
- Configuring HTTPS Mutual Authentication to Improve Service Security
- Using ELB to Redirect HTTP Requests to an HTTPS Listener for Higher Service Security
-
API Reference
- Before You Start
- API Overview
- Calling APIs
-
APIs (V3)
- API Version
- Quota
- AZ
- Load Balancer Flavor
- Reserved IP Address
-
Load Balancer
- Creating a Load Balancer
- Querying Load Balancers
- Viewing Details of a Load Balancer
- Updating a Load Balancer
- Deleting a Load Balancer
- Deleting a Load Balancer and Its Associated Resources
- Querying the Status Tree of a Load Balancer
- Deploying a Load Balancer in Other AZs
- Removing a Load Balancer from AZs
- Certificate
- Security Policy
- IP Address Group
- Listener
- Backend Server Group
- Backend Server
- Health Check
- Forwarding Policy
- Forwarding Rule
- Active/Standby Backend Server Group
- Log
- API (V2)
-
API (OpenStack API)
-
Tag
- Adding a Tag to a Load Balancer
- Batch Adding Load Balancer Tags
- Batch Deleting Load Balancer Tags
- Querying All Tags of a Load Balancer
- Querying the Tags of All Load Balancers
- Querying Load Balancers by Tag
- Deleting a Tag from a Load Balancer
- Adding a Tag to a Listener
- Batch Adding Tags to a Listener
- Batch Deleting Tags from a Listener
- Querying All Tags of a Listener
- Querying the Tags of All Listeners
- Querying Listeners by Tag
- Deleting a Tag from a Listener
- Status Codes
-
Tag
- Examples
- Permissions and Supported Actions
- Appendix
-
Historical APIs
- Shared Load Balancer APIs (OpenStack)
- Asynchronous Job Query
- Querying Versions
-
Getting Started
- Creating a Load Balancer
- Obtaining a Token
- Creating a Load Balancer
- Creating a Public Network Load Balancer
- Adding a Listener
- Creating a Backend Server Group
- Adding Backend Servers
- Configuring a Health Check
- Adding a Forwarding Policy
- Adding a Forwarding Rule
- Adding a Whitelist
- Creating an SSL Certificate
- Cascade Delete
- SDK Reference
-
FAQs
- Popular Questions
-
Service Abnormality
- Why Can't I Access My Backend Servers Through a Load Balancer?
- Why Does a Server Occasionally Time Out When a Client Access It Through Different Load Balancers or Different Listeners of a Load Balancer?
- What Can I Do If ELB Can't Be Accessed or Traffic Routing is Interrupted?
- How Can I Handle Abnormal Status Codes?
- How Do I Handle Abnormal Request Headers?
- How Do I Check for Traffic Inconsistencies?
- Why Does ELB Fail to Distribute Traffic Evenly?
- How Do I Check If There Is Excessive Access Delay?
- What Do I Do If a Load Balancer Fails a Stress Test?
- How Do I Check If Sticky Sessions Failed to Take Effect?
-
ELB Functionality
- Can Load Balancers Be Used Separately?
- Can ELB Block DDoS Attacks and Secure Web Code?
- What Types of APIs Does ELB Provide? What Are Permissions of ELB?
- Can Backend Servers of a Load Balancer Run Different OSs?
- Can ELB Be Used Across Accounts or VPCs?
- Can a Backend Server Access Its Load Balancer?
- Can Both the Listener and Backend Server Group Use HTTPS?
- Does ELB Support IPv6 Networks?
- How Do I Determine the Server Response Time Based on Monitoring Data and Logs?
- How Can I Transfer the IP Address of a Client?
- What Are the Differences Between Persistent Connections and Sticky Sessions?
- How Do I Test Sticky Sessions Using Linux Curl Commands?
-
Load Balancers
- What Is Quota?
- How Does ELB Distribute Traffic?
- How Can I Configure Load Balancing for Containerized Applications?
- Can I Bind Multiple EIPs to a Load Balancer?
- Why Multiple IP Addresses Are Required When I Create a Dedicated Load Balancer?
- Can Backend Servers Access the Internet Using the EIP of the Load Balancer?
- Do Shared Load Balancers Have Specifications?
- What Is the Difference Between the Bandwidth Defined in Each Specification of a Dedicated Load Balancer and the Bandwidth of an EIP?
- How Do I Combine ELB and WAF?
-
Listeners
- What Are the Relationships Between Load Balancing Algorithms and Sticky Session Types?
- Will ELB Stop Distributing Traffic Immediately After a Listener Is Deleted?
- Does ELB Have Restrictions on the File Upload Speed and Size?
- Can Multiple Load Balancers Route Requests to One Backend Server?
- How Is WebSocket Used?
- What Are the Three Timeouts of a Listener and What Are the Default Durations?
- Why Can't I Select the Target Backend Server Group When Adding or Modifying a Listener?
- Why Is There a Security Warning After a Certificate Is Configured for an HTTPS Listener?
- Why Is a Forwarding Policy in the Faulty State?
-
Backend Servers
- Can Backend Servers Access the Internet After They Are Associated with a Load Balancer?
- Can ELB Distribute Traffic Across Servers That Are Not Provided by Huawei Cloud?
- Why Are Backend Servers Frequently Accessed by IP Addresses in 100.125.0.0/16 or 214.0.0.0/8?
- Can ELB Route Traffic Across Regions?
- Does Each Backend Server Need an EIP to Receive Requests from a Public Network Load Balancer?
- How Do I Check the Network Conditions of a Backend Server?
- How Can I Check the Network Configuration of a Backend Server?
- How Do I Check the Status of a Backend Server?
- How Do I Check Whether a Backend Server Can Be Accessed Through an EIP?
- Why Is the Number of Active Connections Monitored by Cloud Eye Different from the Number of Connections Established with the Backend Servers?
- Why Can I Access Backend Servers After a Whitelist Is Configured?
- When Will the Changes to Server Weights Be Applied?
-
Health Checks
- How Do I Troubleshoot an Unhealthy Backend Server of a Dedicated Load Balancer?
- How Do I Troubleshoot an Unhealthy Backend Server of a Shared Load Balancer?
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Different from the Configured Interval?
- How Does ELB Perform UDP Health Checks? What Are the Precautions for UDP Health Checks?
- Why Does ELB Frequently Send Requests to Backend Servers During Health Checks?
- When Does a Health Check Start?
- What Do I Do If a Lot of Access Logs Are Generated During Health Checks?
- What Status Codes Will Be Returned If Backend Servers Are Identified as Healthy?
- Certificates
- Access Logging
- Monitoring
-
Billing
- When Do I Need Public Bandwidth for ELB?
- Will I Be Billed for Both the Bandwidth Used by the Load Balancer and the Bandwidth Used by Backend Servers?
- Do I Need to Adjust the Bandwidth of Shared Load Balancers Based on the Bandwidth Used by Backend Servers?
- Can I Modify the Bandwidth of a Load Balancer?
- What Functions Will Become Unavailable If a Load Balancer Is Frozen?
- Videos
- Glossary
-
More Documents
-
User Guide (ME-Abu Dhabi Region)
- Service Overview
- Load Balancer
- Listener
- Backend Server
- Health Check
- Certificate
- Access Logging
- Monitoring
- Auditing
-
FAQs
- Questions Summary
- ELB Usage
- Load Balancer
- Listener
-
Backend Server
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Is Different from the Configured Health Check Interval?
- Can Backend Servers Access the Public Network After They Are Associated with a Load Balancer?
- How Can I Check the Network Conditions of a Backend Server?
- How Can I Check the Network Configuration of a Backend Server?
- How Can I Check the Status of a Backend Server?
- When Is a Backend Server Considered Healthy?
- Health Check
- Obtaining Source IP Addresses
- HTTP/HTTPS Listeners
- Sticky Session
- Appendix
- Change History
-
API Reference (ME-Abu Dhabi Region)
- Before You Start
- API Overview
- Calling APIs
- Getting Started
- Load Balancer APIs
- Load Balancer (Enterprise Project) APIs
- Common Parameters
- Appendix
- Change History
-
User Guide (Paris Region)
-
Service Overview
- What Is ELB?
- Product Advantages
- How ELB Works
- Application Scenarios
- Differences Between Dedicated and Shared Load Balancers
- Load Balancing on a Public or Private Network
- Network Traffic Paths
- Specifications of Dedicated Load Balancers
- Quotas and Constraints
- Billing (Shared Load Balancers)
- Billing (Dedicated Load Balancers)
- Permissions
- Product Concepts
- How ELB Works with Other Services
- Getting Started
-
Load Balancer
- Overview
- Preparations for Creating a Load Balancer
- Creating a Dedicated Load Balancer
- Creating a Shared Load Balancer
- Configuring Deletion Protection for Load Balancers
- Modifying the Bandwidth
- Changing the Specifications of a Dedicated Load Balancer
- Changing an IP Address
- Binding an IP Address to or Unbinding an IP Address from a Load Balancer
- Adding to or Removing from an IPv6 Shared Bandwidth
- Exporting the Load Balancer List
- Deleting a Load Balancer
- Listener
- Advanced Features of HTTP/HTTPS Listeners
- Backend Server Group
- Backend Server (Dedicated Load Balancers)
- Backend Server (Shared Load Balancers)
- Certificate
- Access Control
- TLS Security Policy
- Tag
- Access Logging
- Monitoring
- Auditing
- Load Balancer Migration
- Permissions Management
- Quotas
-
FAQ
- Popular Questions
- Why Can't I Access My Backend Servers Through a Load Balancer?
- What Can I Do If ELB Can't Be Accessed or Traffic Routing is Interrupted?
- How Can I Handle Error Codes?
- Can ELB Be Used Separately?
- Does ELB Support Persistent Connections?
- Does ELB Support FTP on Backend Servers?
- Is an EIP Assigned Exclusively to a Load Balancer?
- How Many Load Balancers and Listeners Can I Have?
- What Types of APIs Does ELB Provide? What Are Permissions of ELB?
- Can I Adjust the Number of Backend Servers When a Load Balancer is Running?
- Can Backend Servers Run Different OSs?
- Can I Configure Different Backend Ports for a Load Balancer?
- Can ELB Be Used Across Accounts or VPCs?
- Can Backend Servers Access the Ports of a Load Balancer?
- Can Both the Listener and Backend Server Group Use HTTPS?
- Can I Change the VPC and Subnet for My Load Balancer?
- Can I Upgrade a Shared Load Balancer to a Dedicated Load Balancer Without Interrupting Traffic Routing?
- Does ELB Support IPv6 Networks?
- How Do I Check for Traffic Inconsistencies?
- How Do I Check If Traffic Is Being Evenly Distributed?
- How Do I Check If There Is Excessive Access Delay?
- What Do I Do If a Load Balancer Fails a Stress Test?
-
Load Balancers
- How Does ELB Distribute Traffic?
- How Can I Access a Load Balancer Across VPCs?
- How Can I Configure Load Balancing for Containerized Applications?
- Why Can't I Delete My Load Balancer?
- Do I Need to Configure EIP Bandwidth for My Load Balancers?
- Can I Bind Multiple EIPs to a Load Balancer?
- Why Multiple IP Addresses Are Required When I Create or Enable a Dedicated Load Balancer?
- Why Are Requests from the Same IP Address Routed to Different Backend Servers When the Load Balancing Algorithm Is Source IP Hash?
- Can Backend Servers Access the Internet Using the EIP of the Load Balancer?
- Do Shared Load Balancers Have Specifications?
- Will Traffic Routing Be Interrupted If the Load Balancing Algorithm Is Changed?
- What Is the Difference Between the Bandwidth Included in Each Specification of a Dedicated Load Balancer and the Bandwidth of an EIP?
- How Do I Combine ELB and WAF?
-
Listeners
- What Are the Relationships Between Load Balancing Algorithms and Sticky Session Types?
- Can I Bind Multiple Certificates to a Listener?
- What HTTP Headers Can I Configure for an HTTP and HTTP Listener?
- Will ELB Stop Distributing Traffic Immediately After a Listener Is Deleted?
- Does ELB Have Restrictions on the File Upload Speed and Size?
- Can Multiple Load Balancers Route Requests to One Backend Server?
- How Is WebSocket Used?
- Why Can't I Select the Target Backend Server Group When Adding or Modifying a Listener?
- Why Cannot I Add a Listener to a Dedicated Load Balancer?
-
Backend Servers
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Different from What I Have Configured?
- Can Backend Servers Access the Internet After They Are Associated with a Load Balancer?
- Why Are Backend Servers Frequently Accessed by IP Addresses in 100.125.0.0/16?
- Can ELB Route Traffic Across Regions?
- Does Each Backend Server Need an EIP to Receive Requests from a Public Network Load Balancer?
- How Do I Check the Network Conditions of a Backend Server?
- How Can I Check the Network Configuration of a Backend Server?
- How Do I Check the Status of a Backend Server?
- When Is a Backend Server Considered Healthy?
- How Do I Check Whether a Backend Server Can Be Accessed Through an EIP?
- Why Is the Number of Active Connections Monitored by Cloud Eye Different from the Number of Connections Established with the Backend Servers?
- Why Can I Access Backend Servers After a Whitelist Is Configured?
- When Will Modified Weights Take Effect?
- Why Must the Subnet Where the Load Balancer Resides Have at Least 16 Available IP Addresses for Enabling IP as a Backend?
-
Health Checks
- How Do I Troubleshoot an Unhealthy Backend Server?
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Different from the Configured Interval?
- How Does ELB Perform UDP Health Checks? What Are the Precautions for UDP Health Checks?
- Why Does ELB Frequently Send Requests to Backend Servers During Health Checks?
- When Does a Health Check Start?
- Do Maximum Retries Include Health Checks That Consider Backend Servers Unhealthy?
- What Do I Do If a Lot of Access Logs Are Generated During Health Checks?
- What Status Codes Will Be Returned If Backend Servers Are Identified as Healthy?
- Obtaining Source IP Addresses
-
HTTP/HTTPS Listeners
- Which Protocol Should I Select for the Backend Server Group When Adding an HTTPS Listener?
- Why Is There a Security Warning After a Certificate Is Configured?
- Why Is a Forwarding Policy in the Faulty State?
- Why Can't I Add a Forwarding Policy to a Listener?
- Why Cannot I Select an Existing Backend Server Group When Adding a Forwarding Policy?
- Sticky Sessions
- Certificates
- Monitoring
- Change History
-
Service Overview
-
API Reference (Paris Region)
- Before You Start
- API Overview
- Calling APIs
- Getting Started
- Dedicated Load Balancer APIs
- Classic Load Balancer APIs
- Enhanced Load Balancer APIs
- Appendix
- Change History
-
User Guide (Kuala Lumpur Region)
- Service Overview
- Getting Started
-
Load Balancer
- Overview
- Preparations for Creating a Load Balancer
- Creating a Dedicated Load Balancer
- Modifying the Bandwidth
- Changing the Specifications of a Dedicated Load Balancer
- Changing an IP Address
- Binding an IP Address to or Unbinding an IP Address from a Load Balancer
- Adding to or Removing from an IPv6 Shared Bandwidth
- Exporting the Load Balancer List
- Deleting a Load Balancer
- Listener
- Advanced Features of HTTP/HTTPS Listeners
- Backend Server Group
- Backend Server
- Certificate
- Access Control
- Access Logging
- Monitoring
- Auditing
- Quotas
-
FAQ
- Popular Questions
- Service Abnormality
-
ELB Functionality
- Can ELB Be Used Separately?
- Does ELB Support Persistent Connections?
- Does ELB Support FTP on Backend Servers?
- Is an EIP Assigned Exclusively to a Load Balancer?
- How Many Load Balancers and Listeners Can I Have?
- What Types of APIs Does ELB Provide? What Are Permissions of ELB?
- Can I Adjust the Number of Backend Servers When a Load Balancer is Running?
- Can Backend Servers Run Different OSs?
- Can I Configure Different Backend Ports for a Load Balancer?
- Can ELB Be Used Across Accounts or VPCs?
- Can Backend Servers Access the Ports of a Load Balancer?
- Can Both the Listener and Backend Server Group Use HTTPS?
- Can I Change the VPC and Subnet for My Load Balancer?
- Load Balancing Performance
-
Load Balancers
- How Does ELB Distribute Traffic?
- How Can I Access a Load Balancer Across VPCs?
- Do I Need to Configure EIP Bandwidth for My Load Balancers?
- Can I Bind Multiple EIPs to a Load Balancer?
- Why Multiple IP Addresses Are Required When I Create or Enable a Dedicated Load Balancer?
- Why Are Requests from the Same IP Address Routed to Different Backend Servers When the Load Balancing Algorithm Is Source IP Hash?
- Can Backend Servers Access the Internet Using the EIP of the Load Balancer?
- Will Traffic Routing Be Interrupted If the Load Balancing Algorithm Is Changed?
- What Is the Difference Between the Bandwidth Included in Each Specification of a Dedicated Load Balancer and the Bandwidth of an EIP?
-
Listeners
- What Are the Relationships Between Load Balancing Algorithms and Sticky Session Types?
- Can I Bind Multiple Certificates to a Listener?
- Will ELB Stop Distributing Traffic Immediately After a Listener Is Deleted?
- Does ELB Have Restrictions on the File Upload Speed and Size?
- Can Multiple Load Balancers Route Requests to One Backend Server?
- How Is WebSocket Used?
- Why Can't I Select the Target Backend Server Group When Adding or Modifying a Listener?
- Why Cannot I Add a Listener to a Dedicated Load Balancer?
-
Backend Servers
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Different from What I Have Configured?
- Can Backend Servers Access the Internet After They Are Associated with a Load Balancer?
- Can ELB Route Traffic Across Regions?
- Does Each Backend Server Need an EIP to Receive Requests from a Public Network Load Balancer?
- How Do I Check the Network Conditions of a Backend Server?
- How Can I Check the Network Configuration of a Backend Server?
- How Do I Check the Status of a Backend Server?
- When Is a Backend Server Considered Healthy?
- Why Can I Access Backend Servers After a Whitelist Is Configured?
- When Will Modified Weights Take Effect?
- Why Must the Subnet Where the Load Balancer Resides Have at Least 16 Available IP Addresses for Enabling IP as a Backend?
-
Health Checks
- How Do I Troubleshoot an Unhealthy Backend Server?
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Different from the Configured Interval?
- How Does ELB Perform UDP Health Checks? What Are the Precautions for UDP Health Checks?
- Why Does ELB Frequently Send Requests to Backend Servers During Health Checks?
- When Does a Health Check Start?
- Do Maximum Retries Include Health Checks That Consider Backend Servers Unhealthy?
- What Do I Do If a Lot of Access Logs Are Generated During Health Checks?
- What Status Codes Will Be Returned If Backend Servers Are Identified as Healthy?
- Obtaining Source IP Addresses
-
HTTP/HTTPS Listeners
- Which Protocol Should I Select for the Backend Server Group When Adding an HTTPS Listener?
- Why Is There a Security Warning After a Certificate Is Configured?
- Why Is a Forwarding Policy in the Faulty State?
- Why Can't I Add a Forwarding Policy to a Listener?
- Why Cannot I Select an Existing Backend Server Group When Adding a Forwarding Policy?
- Sticky Sessions
- Certificates
- Monitoring
- Change History
-
API Reference (Kuala Lumpur Region)
- Before You Start
- API Overview
- Calling APIs
- APIs
- Permissions Policies and Supported Actions
- Appendix
- Historical APIs
- Change History
-
User Guide (Ankara Region)
- Service Overview
- Load Balancer
- Listener
- Advanced Features of HTTP/HTTPS Listeners
- Backend Server Group
- Backend Server
- Certificate
- Access Control
- TLS Security Policy
- Access Logging
- Monitoring
- Quotas
-
FAQ
- Popular Questions
-
ELB Functionality
- Can ELB Be Used Separately?
- Does ELB Support Persistent Connections?
- Does ELB Support FTP on Backend Servers?
- Is an EIP Assigned Exclusively to a Load Balancer?
- How Many Load Balancers and Listeners Can I Have?
- What Types of APIs Does ELB Provide? What Are Permissions of ELB?
- Can I Adjust the Number of Backend Servers When a Load Balancer is Running?
- Can Backend Servers Run Different OSs?
- Can I Configure Different Backend Ports for a Load Balancer?
- Can ELB Be Used Across Accounts or VPCs?
- Can Backend Servers Access the Ports of a Load Balancer?
- Can Both the Listener and Backend Server Group Use HTTPS?
- Can I Change the VPC and Subnet for My Load Balancer?
-
Load Balancers
- How Does ELB Distribute Traffic?
- How Can I Access a Load Balancer Across VPCs?
- Do I Need to Configure EIP Bandwidth for My Load Balancers?
- Can I Bind Multiple EIPs to a Load Balancer?
- Why Multiple IP Addresses Are Required When I Create or Enable a Dedicated Load Balancer?
- Why Are Requests from the Same IP Address Routed to Different Backend Servers When the Load Balancing Algorithm Is Source IP Hash?
- Can Backend Servers Access the Internet Using the EIP of the Load Balancer?
- Will Traffic Routing Be Interrupted If the Load Balancing Algorithm Is Changed?
- What Is the Difference Between the Bandwidth Included in Each Specification of a Dedicated Load Balancer and the Bandwidth of an EIP?
-
Listeners
- What Are the Relationships Between Load Balancing Algorithms and Sticky Session Types?
- Can I Bind Multiple Certificates to a Listener?
- Will ELB Stop Distributing Traffic Immediately After a Listener Is Deleted?
- Does ELB Have Restrictions on the File Upload Speed and Size?
- Can Multiple Load Balancers Route Requests to One Backend Server?
- How Is WebSocket Used?
- Why Can't I Select the Target Backend Server Group When Adding or Modifying a Listener?
- Why Cannot I Add a Listener to a Dedicated Load Balancer?
-
Backend Servers
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Different from What I Have Configured?
- Can Backend Servers Access the Internet After They Are Associated with a Load Balancer?
- Can ELB Route Traffic Across Regions?
- Does Each Backend Server Need an EIP to Receive Requests from a Public Network Load Balancer?
- How Do I Check the Network Conditions of a Backend Server?
- How Can I Check the Network Configuration of a Backend Server?
- How Do I Check the Status of a Backend Server?
- When Is a Backend Server Considered Healthy?
- Why Can I Access Backend Servers After a Whitelist Is Configured?
- When Will Modified Weights Take Effect?
- Why Must the Subnet Where the Load Balancer Resides Have at Least 16 Available IP Addresses for Enabling IP as a Backend?
-
Health Checks
- How Do I Troubleshoot an Unhealthy Backend Server?
- Why Is the Interval at Which Backend Servers Receive Health Check Packets Different from the Configured Interval?
- How Does ELB Perform UDP Health Checks? What Are the Precautions for UDP Health Checks?
- Why Does ELB Frequently Send Requests to Backend Servers During Health Checks?
- When Does a Health Check Start?
- Do Maximum Retries Include Health Checks That Consider Backend Servers Unhealthy?
- What Do I Do If a Lot of Access Logs Are Generated During Health Checks?
- What Status Codes Will Be Returned If Backend Servers Are Identified as Healthy?
- Obtaining Source IP Addresses
-
HTTP/HTTPS Listeners
- Which Protocol Should I Select for the Backend Server Group When Adding an HTTPS Listener?
- Why Is There a Security Warning After a Certificate Is Configured?
- Why Is a Forwarding Policy in the Faulty State?
- Why Can't I Add a Forwarding Policy to a Listener?
- Why Cannot I Select an Existing Backend Server Group When Adding a Forwarding Policy?
- Sticky Sessions
- Certificates
- Monitoring
- Change History
-
API Reference (Ankara Region)
- Before You Start
- API Overview
- Calling APIs
- APIs (V3)
- APIs (V2)
-
APIs (OpenStack)
-
Tag
- Adding a Tag to a Load Balancer
- Batch Adding Load Balancer Tags
- Batch Deleting Load Balancer Tags
- Querying All Tags of a Load Balancer
- Querying the Tags of All Load Balancers
- Querying Load Balancers by Tag
- Deleting a Tag from a Load Balancer
- Adding a Tag to a Listener
- Batch Adding Tags to a Listener
- Batch Deleting Tags from a Listener
- Querying All Tags of a Listener
- Querying the Tags of All Listeners
- Querying Listeners by Tag
- Deleting a Tag from a Listener
- Status Codes
-
Tag
- Permissions and Supported Actions
- Appendix
- Change History
-
User Guide (ME-Abu Dhabi Region)
- General Reference
- Symptom
- Background
- Troubleshooting
- Checking Security Group Rules
- Checking Network ACL Rules
- Checking the Health Check Configuration
- Checking Whether the Backend Server Group Is Associated with a Listener
- Checking Whether an EIP or Private IP Address Is Bound to a Load Balancer
- Checking the Backend Server
- Checking the Firewall on the Backend Server
- Checking the Backend Server Route
- Checking the Backend Server Load
- Checking the hosts.deny File
- Submitting a Service Ticket
Show all
Copied.
How Do I Troubleshoot an Unhealthy Backend Server of a Dedicated Load Balancer?
Symptom
If a client cannot access a backend server through a load balancer, the backend server is declared unhealthy. You can view the health check results for a backend server on the ELB console.
If a backend server is considered unhealthy, ELB will not route traffic to it until it is declared healthy again.
Background
To check the health of backend servers, dedicated load balancers use the IP addresses in the backend subnet to send heartbeat requests to the backend servers. For details about how a health check works, see Health Check.
- If health checks are disabled, the load balancer will consider the backend servers healthy by default and route requests to them.
- When the weight of a backend server is set to 0:
- Dedicated load balancer: Requests are not routed to the backend server, even if the backend server is considered healthy.
- Shared load balancer: Requests are not routed to the backend server, and the health check result is unhealthy.
Troubleshooting
You can use ELB self-service troubleshooting to locate and fix unhealthy backend servers. If the faults persist, you can perform further checks based on Table 1.
If you need to change the health check configuration, it takes a while for the changes to be applied. The required time depends on the health check interval and timeout duration.
You can find the health check results in the backend server list of the load balancer.
Method |
Items |
---|---|
Self-service troubleshooting |
|
Other check items |
Checking Whether the Backend Server Group Is Associated with a Listener |
Checking Whether an EIP or Private IP Address Is Bound to a Load Balancer |
|
Checking Security Group Rules
The security group rules of backend servers must allow traffic from the backend subnet where the load balancer resides to the backend server using the health check protocol and over the health check port.
You can view the health check settings on the summary page of the backend server group, and configure health checks on the summary page of the listener.
You can use ELB self-service troubleshooting to check the security group rules configured for backend servers based on Table 2.
Check Item |
Solution |
---|---|
The source IP address configured for the inbound rule |
Ensure that the inbound rules of the security group allow traffic from the backend subnet where the load balancer resides to the backend server using the health check protocol and over the health check port. For details, see configuring security group rules (dedicated load balancers). |
The port configured for the inbound rule |
|
The protocol configured for the inbound rule |
|
The source IP address configured for the outbound rule |
Ensure that the outbound rules of the security group allow traffic from the backend subnet where the dedicated load balancer resides to the backend server using the health check protocol and over the health check port. For details, see configuring security group rules (dedicated load balancers). |
The port configured for the outbound rule |
|
The protocol configured for the outbound rule |
If the load balancer has Layer 4 listeners and IP as a Backend is disabled, network ACL rules and security group rules will not take effect. You can use access control to limit which IP addresses are allowed to access the listener. Learn how to configure access control.
Checking Network ACL Rules
Network ACL rules are optional for subnets. If network ACL rules are configured for the subnets where the backend servers are deployed, the network ACL rules must allow traffic from the backend subnet of the dedicated load balancer to the backend server subnets using the health check protocol and over the health check port.
Default network ACL rules deny all inbound and outbound traffic. You can configure an inbound rule to allow traffic from the backend subnet of the load balancer through the port of the backend server.
You can use ELB self-service troubleshooting to check the network ACL rules configured for backend servers based on Table 3.
Check Item |
Solution |
---|---|
The protocol configured for the inbound rule |
Ensure that the inbound rules of the network ACL allow traffic from the backend subnet of the dedicated load balancer to the backend server subnets using the health check protocol and over the health check port. For details, see Network ACL Rules (Dedicated Load Balancer). |
The source IP address configured for the inbound rule |
|
The source port configured for the inbound rule |
|
The destination address configured for the inbound rule |
|
The destination port configured for the inbound rule |
|
The protocol configured for the outbound rule |
Ensure that the outbound rules of the network ACL allow traffic from the backend subnet of the dedicated load balancer to the backend server subnets using the health check protocol and over the health check port. For details, see Network ACL Rules (Dedicated Load Balancer). |
The source IP address configured for the outbound rule |
|
The source port configured for the outbound rule |
|
The destination address configured for the outbound rule |
|
The destination port configured for the outbound rule |
If the load balancer has Layer 4 listeners and IP as a Backend is disabled, network ACL rules and security group rules will not take effect. You can use access control to limit which IP addresses are allowed to access the listener. Learn how to configure access control.
Checking the Health Check Configuration
- Log in to the management console.
- In the upper left corner of the page, click
and select the desired region and project.
- Click
in the upper left corner to display Service List and choose Networking > Elastic Load Balance.
- In the navigation pane on the left, choose Elastic Load Balance > Backend Server Groups.
- On the Backend Server Groups page, locate the backend server group and click its name.
- On the Summary page, click Health Check on the right.
On the Configure Health Check page, view the parameters in the following table. For details about how to set health check parameters, see Modifying Health Check Settings.
Table 4 Parameters for configuring a health check Parameter
Description
Domain Name
If you use HTTP for health checks and the backend server is configured to verify the Host header, enter the domain name configured for the backend server.
Protocol
The outbound rules of the network ACL do not allow traffic over health check protocol.
Port
Configure the backend port as the health check port by referring to Modifying Health Check Settings.
Path
If HTTP is used for health checks, you must check this parameter. A simple static HTML file is recommended.
NOTE:
- If health check protocol is HTTP and the health check port is normal, change the path or change the health check protocol to TCP.
- Enter an absolute path. The following is an example:
- If the URL is http://www.example.com or http://192.168.63.187:9096, enter / as the health check path.
- If the URL is http://www.example.com/chat/try/, enter /chat/try/ as the health check path.
- If the URL is http://192.168.63.187:9096/chat/index.html, enter /chat/index.html as the health check path.
Checking Whether the Backend Server Group Is Associated with a Listener
Check whether the backend server group that contains unhealthy backend servers is associated with a listener by referring to Viewing a Backend Server Group.
If the backend server group is not associated with a listener, health checks may fail.
If the backend server group has been associated with a listener, proceed with the following possible reasons.
Checking Whether an EIP or Private IP Address Is Bound to a Load Balancer
- Check this only when you add a TCP or UDP listener to the load balancer.
If you add a TCP or UDP listener to the load balancer, check whether the load balancer has a private IP address or an EIP bound.
When you create a load balancer for the first time, if no EIP or private IP address is bound to the load balancer, the health check result of backend servers associated with a TCP or UDP listener is Unhealthy.
Checking the Backend Server
If the backend server runs on Windows, use a browser to access https://{Backend server IP address}:{Health check port}. If a 2xx or 3xx code is returned, the backend server is running normally.
- Run the following command on the backend server to check whether the health check port is listened on:
netstat -anlp | grep port
If the health check port and LISTEN are displayed, the health check port is in the listening state. As shown in Figure 1, TCP port 880 is listened on.
If you do not specify a health check port, backend ports are used by default.Figure 2 Backend server port not listened onIf the health check port is not in the listening state, the backend server is not listened on. You need to start the application on the backend server and check whether the health check port is listened on.
- For HTTP health checks, run the following command on the backend server to check the status code:
curl Private IP address of the backend server:Health check port/Health check path -iv
To perform an HTTP health check, the load balancer initiates a GET request to the backend server. If the following response status codes are displayed, the backend server is considered healthy:
TCP listeners: 200
Dedicated load balancers: 200 for HTTP/HTTPS health checks
Figure 3 Unhealthy backend serverFigure 4 Healthy backend server - If the HTTP health check is abnormal, configure a TCP health check. The procedure is described as follows:
On the Listeners tab page, modify the target listener, select the backend server group for which TCP health check has been configured, or add a backend server group and select TCP as the health check protocol. After you complete the configuration, wait for a while and check the health check result.
Checking the Firewall on the Backend Server
If the firewall or other security software is enabled for the backend server, the software may block the IP addresses from the subnet where the load balancer works.
Configure inbound firewall rules to allow traffic from the backend subnet where the load balancer works to backend servers.
Checking the Backend Server Route
Check whether the default route configured for the primary NIC (for example, eth0) has been manually modified. If the default route is changed, health check packets may fail to reach the backend server.
ip route
Alternatively, run the following command:
route -n
Figure 5 shows the command output when the backend server route is normal.
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If the command output does not contain the first route, or the route does not point to the gateway, configure or modify the default route to point to the gateway.
Checking the Backend Server Load
View the vCPU usage, memory usage, network connections of the backend server on the Cloud Eye console to check whether the backend server is overloaded.
If the workloads are high, connections or requests for health checks may time out.
Checking the hosts.deny File
Verify that IP addresses in backend subnet where the load balancer works are not written to the /etc/hosts.deny file on the backend servers.
Submitting a Service Ticket
If the problem persists, submit a service ticket.
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