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Handy Tips and Commands

This document contains a collection of useful tips and commands for working with Kubernetes and Docker.

1. Retrieving YAML Manifests for Existing Resources

If you need the YAML definition for a resource that's already running in your Kubernetes cluster but you don't have the original manifest file, you can retrieve it using kubectl get ... -o yaml.

Example for a Pod:(Replace nginx with your actual pod name and specify a namespace if not default.)

kubectl get po nginx -o yaml > pod.yaml

Example for a DaemonSet (like kube-proxy):

kubectl get ds kube-proxy -n kube-system -o yaml > kube-proxy.yaml

2. Locating Docker Registry Credentials

If you've previously logged into a Docker registry (like Docker Hub) using docker login, Docker stores the authentication credentials (usually an encoded token) in a configuration file.

1. Locate the Docker config file: The file is typically located at ~/.docker/config.json for regular users, or /root/.docker/config.json if you logged in as root.

   cat ~/.docker/config.json
   # Or if you logged in as root:
   # sudo cat /root/.docker/config.json

2. Interpret the auths section: Inside this JSON file, there's an auths section containing entries for each registry you've logged into. The auth field for a registry typically holds a base64 encoded string, which is often username:password (for older setups) or more commonly an access token.

   Example config.json snippet:

   {
     "auths": {
       "https://index.docker.io/v1/": {
         "auth": "dXNlcm5hbWU6cGFzc3dvcmQ="
         // This is an example, your auth string will be different
       }
     }
   }

3. Decode the auth string: To decode it, copy the auth string and use base64 -d.

   # Replace YOUR_AUTH_STRING with the actual string from your config.json
   echo "YOUR_AUTH_STRING" | base64 -d
   # This will output the decoded credentials, often in the format 'username:token' or 'username:password'.

   Note: Handling these credentials carefully is important for security.

3. Quickly Create a Service Account with Cluster Admin Privileges

For testing or development purposes, you might need a Service Account (SA) with broad permissions. Warning: Granting cluster-admin privileges is powerful and should be done with extreme caution, especially in production environments.

1. Create a Service Account: (Assuming in the default namespace, or specify -n <your-namespace>)

   kubectl create sa demo

2. Create a ClusterRoleBinding: This command binds the cluster-admin ClusterRole to the demo Service Account in the default namespace.

   kubectl create clusterrolebinding sa-demo-cluster-admin-binding \
     --clusterrole=cluster-admin \
     --serviceaccount=default:demo

   (Changed binding name to be more descriptive and less likely to conflict if sa-demo was used for a namespaced RoleBinding elsewhere.)

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