Planning CIDR Blocks for a Cluster
Before creating a cluster on CCE, determine the number of VPCs, number of subnets, container CIDR blocks, and Services for access based on service requirements.
This topic describes the addresses in a CCE cluster in a VPC and how to plan CIDR blocks.
Constraints
To access a CCE cluster through a VPN, ensure that the VPN does not conflict with the VPC CIDR block where the cluster resides and the container CIDR block.
Basic Concepts
- VPC CIDR Block
Virtual Private Cloud (VPC) enables you to provision logically isolated, configurable, and manageable virtual networks for cloud servers, cloud containers, and cloud databases. You have complete control over your virtual network, including selecting your own CIDR block, creating subnets, and configuring security groups. You can also assign EIPs and allocate bandwidth in your VPC for secure and easy access to your business system.
- Subnet CIDR Block
A subnet is a network that manages ECS network planes. It supports IP address management and DNS. The IP addresses of all ECSs in a subnet belong to the subnet.Figure 1 VPC CIDR block architecture
By default, ECSs in all subnets of the same VPC can communicate with one another, while ECSs in different VPCs cannot communicate with each other.
You can create a peering connection on VPC to enable ECSs in different VPCs to communicate with each other.
- Container (Pod) CIDR Block
Pod is a Kubernetes concept. Each pod has an IP address.
When creating a cluster on CCE, you can specify the pod (container) CIDR block, which cannot overlap with the subnet CIDR block. For example, if the subnet CIDR block is 192.168.0.0/16, the container CIDR block cannot be 192.168.0.0/18 or 192.168.1.0/18, because these addresses are included in 192.168.0.0/16.
- Container Subnet (Only for CCE Turbo Clusters)
In a CCE Turbo cluster, a container is assigned an IP address from the CIDR block of a VPC. The container subnet can overlap with the subnet CIDR block. Note that the subnet you select determines the maximum number of pods in the cluster. After a cluster is created, you can only add container subnets but cannot delete them.
- Service CIDR Block
Service is also a Kubernetes concept. Each Service has an address. When creating a cluster on CCE, you can specify the Service CIDR block. Similarly, the Service CIDR block cannot overlap with the subnet CIDR block or the container CIDR block. The Service CIDR block can be used only within a cluster.
Single-VPC Single-Cluster Scenarios
- VPC CIDR Block: specifies the VPC CIDR block where the cluster resides. The size of this CIDR block affects the maximum number of nodes that can be created in the cluster.
- Subnet CIDR Block: specifies the subnet CIDR block where the node in the cluster resides. The subnet CIDR block is included in the VPC CIDR block. Different nodes in the same cluster can be allocated to different subnet CIDR blocks.
- Container CIDR Block: cannot overlap with the subnet CIDR block.
- Service CIDR Block: cannot overlap with the subnet CIDR block or the container CIDR block.
- VPC CIDR Block: specifies the VPC CIDR block where the cluster resides. The size of this CIDR block affects the maximum number of nodes that can be created in the cluster.
- Subnet CIDR Block: specifies the subnet CIDR block where the node in the cluster resides. The subnet CIDR block is included in the VPC CIDR block. Different nodes in the same cluster can be allocated to different subnet CIDR blocks.
- Container Subnet CIDR Block: The container subnet is included in the VPC CIDR block and can overlap with the subnet CIDR block or even be the same as the subnet CIDR block. Note that the container subnet size determines the maximum number of containers in the cluster because IP addresses in the VPC are directly allocated to containers. After a cluster is created, you can only add container subnets but cannot delete them. Set a larger IP address segment for the container subnet to prevent insufficient container IP addresses.
- Service CIDR Block: cannot overlap with the subnet CIDR block or the container CIDR block.
Single-VPC Multi-Cluster Scenarios
VPC network model
- VPC CIDR Block: specifies the VPC CIDR block where the cluster resides. The size of this CIDR block affects the maximum number of nodes that can be created in the cluster.
- Subnet CIDR Block: The subnet CIDR block in each cluster cannot overlap with the container CIDR block.
- Container CIDR Block: If multiple VPC network model clusters exist in a single VPC, the container CIDR blocks of all clusters cannot overlap because the clusters use the same routing table. In this case, if the node security group allows container CIDR block from the peer cluster, pods in one cluster can directly access pods in another cluster through the pod IP addresses.
- Service CIDR Block: can be used only in clusters. Therefore, the Service CIDR blocks of different clusters can overlap, but cannot overlap with the subnet CIDR block and container CIDR block of the cluster.
Tunnel network model
- VPC CIDR Block: specifies the VPC CIDR block where the cluster resides. The size of this CIDR block affects the maximum number of nodes that can be created in the cluster.
- Subnet CIDR Block: The subnet CIDR block in each cluster cannot overlap with the container CIDR block.
- Container CIDR Block: The container CIDR blocks of all clusters can overlap. In this case, pods in different clusters cannot be directly accessed through pod IP addresses. Pods in different clusters need to access each other through Services. The LoadBlancer Services are recommended.
- Service CIDR Block: can be used only in clusters. Therefore, the Service CIDR blocks of different clusters can overlap, but cannot overlap with the subnet CIDR block and container CIDR block of the cluster.
Cloud Native Network 2.0 Model (CCE Turbo Clusters)
- VPC CIDR Block: specifies the VPC CIDR block where the cluster resides. In a CCE Turbo cluster, the CIDR block size affects the total number of nodes and containers that can be created in the cluster.
- Subnet CIDR Block: There is no special restriction on the subnet CIDR blocks in CCE Turbo clusters.
- Container Subnet: The CIDR block of the container subnet is included in the VPC CIDR block. Container subnets in different clusters can overlap with each other or overlap with the subnet CIDR block. However, you are advised to stagger the container CIDR blocks of different clusters and ensure that the container subnet CIDR blocks have sufficient IP addresses. In this case, if the ENI security group of the cluster allows the container CIDR block of the peer cluster, pods in different clusters can directly access each other through IP addresses.
- Service CIDR Block: can be used only in clusters. Therefore, the Service CIDR blocks of different clusters can overlap, but cannot overlap with the subnet CIDR block and container subnet CIDR block of the cluster.
Clusters using different networks
When a VPC contains clusters created with different network models, comply with the following rules when creating a cluster:
- VPC CIDR Block: In this scenario, all clusters are located in the same VPC CIDR block. Ensure that there are sufficient available IP addresses in the VPC.
- Subnet CIDR Block: Ensure that the subnet CIDR block does not overlap with the container CIDR block. Even in some scenarios (for example, coexistence with CCE Turbo clusters), the subnet CIDR block can overlap with the container (subnet) CIDR block. However, this is not recommended.
- Container CIDR Block: Ensure that the container CIDR blocks of clusters in VPC network model do not overlap.
- Service CIDR Block: The Service CIDR blocks of all clusters can overlap, but cannot overlap with the subnet CIDR block and container CIDR block of the cluster.
Cross-VPC Cluster Interconnection
If VPCs cannot communication each other, a VPC peering connection is used to ensure communication between VPCs. When two VPC networks are interconnected, you can configure the packets to be sent to the peer VPC in the route table.
Clusters using VPC networks
To allow clusters that use VPC networks to access each other across VPCs, add routes to the two ends of the VPC peering after a VPC peering connection is created.
When creating a VPC peering connection between containers across VPCs, pay attention to the following points:
- The VPC to which the clusters belong must not overlap. In each cluster, the subnet CIDR block cannot overlap with the container CIDR block.
- The container CIDR blocks of clusters at both ends cannot overlap, but the Service CIDR blocks can.
- If the request end cluster uses the VPC network, check whether the node security group in the destination cluster allows the container CIDR block of the request end cluster. If yes, pods in one cluster can directly access pods in another cluster through the pod IP address. Similarly, if nodes running in the clusters at the two ends of the VPC peering connection need to access each other, the node security group must allow the VPC CIDR block of the peer cluster.
- Add not only the peer cluster VPC CIDR block but also the peer container CIDR block to the VPC routing tables at both ends. Note that this operation must be performed in the VPC route tables of the clusters.
Clusters using tunnel networks
To allow clusters that use tunnel networks to access each other across VPCs, add routes to the two ends of the VPC peering after a VPC peering connection is created.
Pay attention to the following:
- The VPCs of the peer clusters must not overlap.
- The container CIDR blocks of all clusters can overlap, so do the Service CIDR blocks.
- If the request end cluster uses the tunnel network, check whether the node security group in the destination cluster allows the VPC CIDR block (including the node subnets) of the request end cluster. If yes, nodes in one cluster can access nodes in another cluster. However, pods in different clusters cannot be directly accessed using pod IP addresses. Access between pods in different clusters requires Services. The LoadBlancer Services are recommended.
- Add the peer cluster VPC CIDR block to the VPC routing tables at both ends. Note that this operation must be performed in the VPC route tables of the clusters.
Clusters using Cloud Native 2.0 networks (CCE Turbo clusters)
- The VPCs of the clusters at the two ends must not overlap.
- If the request end cluster uses the Cloud Native 2.0 network, check whether the ENI security group (named in the format of {Cluster name}-cce-eni-{Random ID}) of the destination cluster allows the VPC CIDR block (including the node subnets and container CIDR block) of the request end cluster. If yes, pods in one cluster can directly access pods in another cluster through the pod IP addresses. Similarly, if nodes in the clusters at the two ends of the VPC peering need to access each other, allow the VPC CIDR block of the peer cluster in the node security group (named in the format of {Cluster name}-cce-node-{Random ID}).
- Add the peer cluster VPC CIDR block to the VPC routing tables at both ends. Note that this operation must be performed in the VPC route tables of the clusters.
Clusters using different networks
If clusters using different networks need to communicate with each other across VPCs, every one of them may serve as the request end or destination end. Pay attention to the following:
- The VPC CIDR block to which the cluster belongs cannot overlap with the VPC CIDR block of the peer cluster.
- Cluster subnet CIDR blocks cannot overlap with the container CIDR blocks.
- Container CIDR blocks in different clusters cannot overlap with each other.
- If pods or nodes in different clusters need to access each other, the security groups of the clusters on both ends must allow the corresponding CIDR blocks based on the following rules:
- If the request end cluster uses the VPC network, the node security group of the destination cluster must allow the VPC CIDR block (including the node subnets and container CIDR block) of the request end cluster.
- If the request end cluster uses the tunnel network, the node security group of the destination cluster must allow the VPC CIDR block (including the node subnets) of the request end cluster.
- If the request end cluster uses the Cloud Native 2.0 network, the ENI security group and node security group of the destination cluster must allow the VPC CIDR block (including node subnets and container CIDR block) of the request end cluster.
- Add the peer cluster VPC CIDR block to the VPC routing tables at both ends. Note that this operation must be performed in the VPC route tables of the clusters.
If a cluster uses the VPC network, the VPC routing tables at both ends must contain its container CIDR block.
VPC-IDC Scenarios
Similar to the VPC interconnection scenario, some CIDR blocks in the VPC are routed to the IDC. The pod IP addresses of CCE clusters cannot overlap with the addresses within these CIDR blocks. To access the pod IP addresses in the cluster in the IDC, configure the route table to the private line VBR on the IDC.
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