Etcd Backup and Restore (3)

Last post I have show steps to restore etcd, but when we edit the /etc/kubernetes/manifest/etcd.yaml file, there are some confuse among the /var/lib/etcd on hostPath and mountVolumne, the --data-dir in the

etcdctl snapshot restore --data-dir

and the commands inside the /etc/kubernetes/manifest/etcd.yaml file. So here let's give a more detailed explanation.

1. 
   Saving the snapshot
   

etcdctl snapshot save ./stored.db ...

• This command connects to the running etcd


• Takes a snapshot of its current state


• Saves it as stored.db in current directory on host machine

1. 
   Restoring the snapshot
   

etcdctl snapshot restore ./stored.db --data-dir /var/lib/etcd-restore

• Takes the stored.db snapshot file


• Unpacks/expands it into a complete etcd data directory structure


• Places this expanded data directory at /var/lib/etcd-restore on host machine


• This directory now contains all the database files etcd needs to run

1. 
   Container mounting and startup
   

# In etcd.yaml

volumes:

- hostPath:

    path: /var/lib/etcd-restore  # Host machine directory

    type: DirectoryOrCreate

  name: etcd-data

...

volumeMounts:

- mountPath: /var/lib/etcd      # Container directory

  name: etcd-data

• When etcd pod starts, Kubernetes:
  
  
  
  
  1. Sees the hostPath volume configuration
  
  
  2. Mounts host's /var/lib/etcd-restore directory
  
  
  3. Makes it appear at /var/lib/etcd inside container
  
  
  
  

1. 
   etcd process startup
   

command:

- etcd

- --data-dir=/var/lib/etcd

• etcd process starts inside container


• Looks for its data at /var/lib/etcd (which is actually host's /var/lib/etcd-restore mounted)


• Finds and uses the restored data

So the complete data path is:

1. stored.db (snapshot file)

   ↓

2. /var/lib/etcd-restore/* (expanded data on host)

   ↓ (mount)

3. /var/lib/etcd/* (same data, visible in container)

   ↓ (etcd process)

4. Running etcd using restored data