To help you guarantee that your applications stably and reliably run in Kubernetes, this topic describes the recommended Kubernetes cluster configurations.
Set the disk type and size
Select the disk type
- We recommend that you select the SSD disk type.
- For Worker nodes, we recommend that you select the Attach Data Disk check box when you create a cluster. This disk is provided exclusively for the /var/lib/docker file to store local images. It is designed to allow the root disk to store a massive number of images. After your cluster has run for a period, many images you no longer require remain stored. To quickly solve this, we recommend that you take the machine offline, rebuild this disk, and then bring the machine back online.
Set the disk size
Kubernetes nodes require a large disk space because the Docker images, system logs, and application logs are stored in the disk. When creating a Kubernetes cluster, you need to consider the number of pods on each node, the log size of each pod, the image size, the temporary data size, and the space required for system reserved values.
We recommend that you reserve a space of 8 GiB for the ECS instance operation system because the operation system requires a disk space of at least 3 GiB. Kubernetes resource objects then use the remaining disk space.
Whether to build Worker nodes when creating your cluster
- Pay-As-You-Go, indicates that you can build Worker nodes when creating a cluster.
- Subscription, indicates that you can purchase ECS instances as needed and add the instances to your cluster after you create you cluster.
Configure your cluster network settings
- If you want to connect your cluster with services outside Kubernetes, for example, Relational Database Service (RDS), we recommend that you use an existing VPC, rather than create a VPC. This is because VPCs are logically isolated. You can create a VSwitch and add the ECS instances that run Kubernetes to the VSwitch.
- You can select the Terway network plugin or the Flannel network plugin when creating a Kubernetes cluster. For more information, see Flannel and Terway.
- We recommend that you do not set a small CIDR block of the pod network that only supports a minimal number of nodes. The CIDR block setting of the pod network is associated with the Pod Number for Node setting in Advanced Config. For example, if you set the CIDR block of the pod network to X.X.X.X/16, it means that the number of IP addresses assigned to your cluster is 256*256. Additionally, if you set the number of pods on each node to 128, it means that the maximum number of nodes supported by your cluster is 512.
Use multiple zones
Alibaba Cloud supports multiple regions and each region supports multiple zones. Zones are physical areas that have independent power grids and networks within a region. Using multiple zones enables disaster recovery across areas, but increases network latency.
Claim resources for each pod
When you use a Kubernetes cluster, a common problem is that too many pods are scheduled to one node. This scheduling of pods overloads the node, making it unable to provide services.
We recommend that you specify the resource request parameter and the resource limit parameter when configuring a pod in Kubernetes. This recommended configuration enables Kubernetes to select a node with sufficient resources according to the pod resource requirements during the pod deployment. The following example claims that the Nginx pod uses 1-core CPU and 1024 MiB memory, and the pod cannot use more than 2-core CPU or 4096 MiB memory.
apiVersion: v1 kind: Pod metadata: name: nginx spec: containers: - name: nginx image: nginx Resources: # Resource claim. requests: memory: "1024Mi" cpu: "1000m" limits: memory: "4096Mi" cpu: "2000m"
Kubernetes uses a static resource scheduling method, which means that instead of using
the resources that have been used to calculate the remaining resources on each node,
it uses allocated resources. Its calculation method is:
the remaining resources = the total resources - the resources that have been allocated. If you manually run a resource-consuming program, Kubernetes is not aware of the
resources that are being used by the program.
Therefore, you must claim resources for all pods. For the pods that do not have resource claims, after they are scheduled to a node, Kubernetes assumes that the resources used by them on the corresponding node are still available. Therefore, too many pods may be scheduled to this node.
Configure cluster operation and maintenance settings
- Enable Log Service
When creating a cluster, select the Using Log Service check box.
- Configure cluster monitoring
Alibaba Cloud Container Service is integrated with CloudMonitor. By configuring monitoring on nodes, you can implement real-time monitoring. By adding monitoring alarm rules, you can quickly locate the issues that cause abnormal resource usage.When you create a Kubernetes cluster through Container Service, two application groups are automatically created in CloudMonitor: one for Master nodes and one for Worker nodes. You can add alarm rules under these two groups and these rules apply to all machines in the groups. When subsequent nodes are added to the corresponding group, the alarm rules in the group are automatically applied.This means that you only need to configure alarm rules for the ECS resources.Note
- To monitor ECS instances, you need to set alarm rules for resources such as CPU, memory, and disk. We recommend that you set the /var/lib/docker file on an exclusive disk.
Set an application to wait for its dependent application after it starts
Some applications may have some external dependencies. For example, an application may need to read data from a database (DB) or access the interface of another service. However, when the application starts, the DB or the interface may not be available. In traditional manual O&M, if the external dependencies of an application are unavailable when the application starts, the application exits directly.This is known as failfast. This strategy is not applicable for Kubernetes, because O&M in Kubernetes is automated and does not require manual intervention. For example, when you deploy an application, you do not need to manually select a node or start the application on the node. If the application fails, Kubernetes automatically restarts it. Additionally, automatic capacity increase is supported through HPA when large loads occur.
For example, assume that application A depends on application B, and these two applications run on the same node. After the node restarts, application A starts, but application B has not started. In this case, the dependency of application A is unavailable. According to the strategy of failfast, application A exists and will not start even after application B starts. In this case, application A must be started manually.
In Kubernetes, you can set the system to check the dependency of the application during startup, and to implement polling to wait until the dependency is available. This can be implemented throughInit Container.
Set the pod restart policy
When a bug in the code or excessive memory consumption causes application processes to fail, the pod in which the processes reside also fails. We recommend that you set a restart policy for the pod so that the pod can automatically restart after failure.
apiVersion: v1 kind: Pod metadata: name: tomcat spec: containers: - name: tomcat image: tomcat restartPolicy: OnFailure #
Available values of the restart policy parameter are:
- Always: indicates to always restart the pod automatically.
- OnFailure: indicates to automatically restart the pod when the pod fails (the exiting status of the process is not 0).
- Never: indicates to never restart the pod.
Configure the liveness probe and readiness probe
A running pod may not necessarily be able to provide services because processes in the pod may be locked. However, Kubernetes does not automatically restart the pod because the pod is still running. Therefore, you must configure the liveness probe in each pod to determine whether the pod is alive, and whether it can provide services. Then, Kubernetes restarts the pod when the liveness probe detects any exception.
The readiness probe is used to detect whether the pod is ready to provide services. It takes some time for an application to initialize during startup. During the initialization, the application cannot provide services. The readiness probe can determine when the pod is ready to receive traffic from Ingress or Service. When the pod is faulty, the readiness probe stops new traffic being forwarded to the pod.
apiVersion: v1 kind: Pod metadata: name: tomcat spec: containers: - name: tomcat image: tomcat livenessProbe: httpGet: path: /index.jsp port: 8080 initialDelaySeconds: 3 periodSeconds: 3 readinessProbe: httpGet: path: /index.jsp port: 8080
Set one process to run in each container
- It becomes complex to determine the resource usage of the pod as a whole, and it becomes difficult for the resource limit that you set to take effect.
- If only one process runs in a container, the container engine can detect process failures and it restarts the container upon each process failure. However, if multiple processes are put into a container, the container engine cannot determine the failure of any single process. Therefore, the engine does not restart the container when a single process fails even though the container does not work normally.
If you want to run multiple processes simultaneously, Kubernetes can help you easily implement that. For example, nginx and php-fpm communicate with each other through a Unix domain socket. You can use a pod that contains two containers, and put the Unix socket into a shared volume of the two containers.
Avoid Single Point of Failure (SPOF)
If an application uses only one ECS instance, the application is unavailable during the period when Kubernetes restarts the instance upon an instance failure. This issue also occurs when you release an updated version of the application. Therefore, we recommend that you do not directly use pods in Kubernetes. Instead, deploy Deployment or StatefulSet applications and set more than two pods for each application.