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Cheedge Lee
Cheedge Lee

Posted on • Edited on • Originally published at notes-renovation.hashnode.dev

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 items among the /var/lib/etcd on hostPath and mountVolumne.

For example, the --data-dir in the command:

etcdctl snapshot restore --data-dir
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this is the dir on the host machine.

And the parameter also appear inside the /etc/kubernetes/manifest/etcd.yaml file. This is the command running inside the container, so they are totally diffferent. So here let's give a more detailed explanation.

  1. Saving the snapshot 
etcdctl snapshot save ./stored.db ...
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  • 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
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  • 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 # make a new dir for Host machine to use it for store etcd data type: DirectoryOrCreate name: etcd-data ... volumeMounts: - mountPath: /var/lib/etcd # Container directory name: etcd-data
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  • 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
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  • 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
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