Скачать или смотреть Resolving Kubernetes Networking Issues: Why Your Pods Can't Reach Nodes

Discover how to troubleshoot and fix your Kubernetes pod networking issues, especially when using Calico as the CNI. Learn why your pods can't reach nodes and how changing your pod CIDR can solve the problem.
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Resolving Kubernetes Networking Issues: Why Your Pods Can't Reach Nodes

In the sprawling landscape of Kubernetes, pod networking issues can create a significant roadblock. One common issue faced by developers is when pods cannot reach the nodes of the Kubernetes cluster. Such problems can stem from a variety of factors, particularly when using a Container Network Interface (CNI) like Calico.

In this guide, we will explore a specific case where the calico-kube-controllers fails due to the inability to reach the internal Kubernetes service endpoint at 10.96.0.1:443. We will examine the symptoms, errors, and ultimately provide a practical solution to resolve the issue.

Background: The Problem

Recently, a user faced an issue with a newly set-up Kubernetes cluster consisting of 3 master nodes and 7 worker nodes. They had deployed Calico as their network plugin, but encountered the following problems:

The calico-kube-controllers pod was in a CrashLoopBackOff state, indicating repeated failures.

An error in the logs revealed that the pod could not connect to the API server at 10.96.0.1:443, which is a standard cluster IP for Kubernetes services.

When running the command wget -S 10.96.0.1:443 from within a node, they received a response. However, the same command executed from a pod resulted in a timeout error.

They noted that pods were unable to ping nodes, indicating severe connectivity issues within the cluster.

Diagnosis: What Went Wrong?

The errors indicated that:

Networking Configuration Issues: The problem was primarily related to the networking setup, specifically how Calico was interacting with the created Pod Network.

Inaccessible Cluster IPs: While nodes could connect to the service IP, the reverse was not true—thus causing pods unable to reach out to the cluster APIs and nodes.

The Solution: Changing the Pod CIDR

In troubleshooting this issue, the underlying root cause was determined to be the Pod CIDR (Classless Inter-Domain Routing) configuration. The user successfully resolved the issue by recreating the Kubernetes cluster with a different Pod CIDR.

Steps Taken to Resolve:

Backup Configuration: Before making any changes, ensure you have a backup of your Kubernetes configurations and any relevant data.

Recreate the Cluster:

Use a different Pod CIDR that is not conflicting with existing IP ranges in your network (e.g., 10.244.0.0/16 or 192.168.100.0/16 depending on your environment).

Deploy Calico: Once the cluster is recreated:

Install Calico and monitor the deployment of the calico-kube-controllers to ensure there are no errors.

Verify Connectivity:

Confirm that pods can now successfully connect to the service IPs and the nodes.

Use commands such as ping, wget, or other verification tools from within the pods to check connectivity.

Why a Different Pod CIDR?

Changing the Pod CIDR can mitigate the issue by ensuring that the generated pod IPs do not overlap with existing IPs in the host or any conflict-prone areas of the network. This change allows seamless routing and communication between nodes and pods.

Conclusion

Networking issues can be tricky when working with Kubernetes, especially when deploying network solutions like Calico. However, understanding how to diagnose core issues and knowing how to reconfigure the network settings, such as the Pod CIDR, can lead to successful resolution.

If you are experiencing similar issues, remember to carefully inspect your network configurations and consider the steps outlined above. Happy K8s clustering!