Connecting to a DB Instance from a Linux ECS

Step 1: Buy an ECS

1. Log in to the management console and check whether there is an ECS available.
   • If there is a Linux ECS, go to 3.
   • If no Linux ECS is available, go to 2.
   Figure 1 ECS
   
2. Buy an ECS and select Linux (for example, CentOS) as its OS.

   To download a PostgreSQL client to the ECS, bind an EIP to the ECS. The ECS must be in the same region, VPC, and security group as the RDS for PostgreSQL DB instance for mutual communications.

   For details about how to purchase a Linux ECS, see "Purchasing an ECS" in Elastic Cloud Server Getting Started.

3. On the ECS Information page, view the region and VPC of the ECS.
   Figure 2 ECS information
   

4. On the Overview page of the RDS for PostgreSQL instance, view the region and VPC of the DB instance.
   Figure 3 Overview
   
5. Check whether the ECS and RDS for PostgreSQL instance are in the same region and VPC.
   • If yes, go to Step 2: Test Connectivity and Install a PostgreSQL Client.
   • If they are not in the same region, purchase another ECS or DB instance. The ECS and DB instance in different regions cannot communicate with each other. To reduce network latency, deploy your DB instance in the region nearest to your workloads.
   • If the ECS and DB instance are in different VPCs, change the VPC of the ECS to that of the DB instance. For details, see Changing a VPC.

Step 2: Test Connectivity and Install a PostgreSQL Client

1. Log in to the ECS. For details, see Login Using VNC in the Elastic Cloud Server User Guide.
2. On the Instances page of the RDS console, click the DB instance name.
3. Choose Connectivity & Security from the navigation pane. In the Connection Information area, obtain the floating IP address and database port of the DB instance.
   Figure 4 Connection information
   
4. On the ECS, check whether the floating IP address and database port of the DB instance can be connected.

   telnet 192.168.0.7 5432

   • If yes, network connectivity is normal.
   • If no, check the security group rules.
     • If in the security group of the ECS, there is no outbound rule with Destination set to 0.0.0.0/0 and Protocol & Port set to All, add an outbound rule for the floating IP address and port of the DB instance.
       Figure 5 ECS security group
       
     • If in the security group of the DB instance, there is no inbound rule with Source set to 0.0.0.0/0 and Protocol & Port set to All, add an inbound rule for the private IP address and port of the ECS. For details, see Configuring Security Group Rules.
       Figure 6 DB instance security group
       
5. Open the client installation page.

   PostgreSQL provides client installation methods for different OSs on its official website.

   The following describes how to install a PostgreSQL 12 client in CentOS.

6. Select a DB engine version, OS, and OS architecture, and run the following commands on the ECS to install a PostgreSQL client:

   sudo yum install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm

   Figure 7 Installing a client
   
   • Select a DB engine version that is consistent with that of your RDS for PostgreSQL instance.
   • Select an OS that is consistent with that of the ECS.
   • Select an OS architecture that is consistent with that of the ECS.
   Figure 8 Installing the RPM package
   
   Figure 9 Client installed
   

Step 3: Connect to the DB Instance Using Commands (SSL Connection)

1. On the Instances page, click the DB instance name.
2. In the navigation pane, choose Connectivity & Security.
3. In the Connection Information area, click next to the SSL field to download Certificate Download.zip, and extract the root certificate ca.pem and bundle ca-bundle.pem from the package.
   Figure 10 Downloading a certificate
   
4. Upload ca.pem to the ECS.
   

   • TLS v1.2 or later is recommended. Versions earlier than TLS v1.2 have security risks.
   • The recommended protocol algorithm is EECDH+ECDSA+AESGCM:EECDH+aRSA+AESGCM:EDH+aRSA+AESGCM:EDH+aDSS+AESGCM:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!SRP:!RC4. Using other options have security risks.
   • ca-bundle.pem contains both the new certificate provided as of April 2017 and the old certificate.
   • Both ca.pem and ca-bundle.pem can be used for SSL connections because ca-bundle.pem contains ca.pem.
5. Run the following command on the ECS to connect to the DB instance:

   psql --no-readline -h <host> -p <port> "dbname=<database> user=<user> sslmode=verify-ca sslrootcert=<ca-file-directory>"

   Example:

   psql --no-readline -h 192.168.0.7 -p 5432 "dbname=postgres user=root sslmode=verify-ca sslrootcert=/root/ca.pem"

   Table 1 Parameter description

   Parameter	Description
   <host>	Floating IP address obtained in 3.
   <port>	Database port obtained in 3. The default value is 5432.
   <database>	Name of the database to be connected. The default database name is postgres.
   <user>	Administrator account root.
   <ca-file-directory>	Directory of the CA certificate used for the SSL connection. This certificate should be stored in the directory where the command is executed.
   sslmode	SSL connection mode. Set it to verify-ca to use a CA to check whether the service is trusted.

6. Enter the password of the database account as prompted.

   Password:

   If the following information is displayed, the connection is successful.

   SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384, bits: 256, compression: off)

Follow-up Operations

After logging in to the DB instance, you can create or migrate databases.

• Creating a PostgreSQL Database Using an API
• Managing PostgreSQL Databases Using DAS
• Migration Solution Overview