etcd-io__etcd/Documentation/learning/api.md

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title: etcd3 API

NOTE: this doc is not finished!

Response header

All Responses from etcd API have a response header attached. The response header includes the metadata of the response.

message ResponseHeader {
  uint64 cluster_id = 1;
  uint64 member_id = 2;
  int64 revision = 3;
  uint64 raft_term = 4;
}

• Cluster_ID - the ID of the cluster that generates the response
• Member_ID - the ID of the member that generates the response
• Revision - the revision of the key-value store when the response is generated
• Raft_Term - the Raft term of the member when the response is generated

An application may read the Cluster_ID (Member_ID) field to ensure it is communicating with the intended cluster (member).

Applications can use the Revision to know the latest revision of the key-value store. This is especially useful when applications specify a historical revision to make time travel query and wishes to know the latest revision at the time of the request.

Applications can use Raft_Term to detect when the cluster completes a new leader election.

Key-Value API

Key-Value API is used to manipulate key-value pairs stored inside etcd. The key-value API is defined as a gRPC service. The Key-Value pair is defined as structured data in protobuf format.

Key-Value pair

A key-value pair is the smallest unit that the key-value API can manipulate. Each key-value pair has a number of fields:

message KeyValue {
  bytes key = 1;
  int64 create_revision = 2;
  int64 mod_revision = 3;
  int64 version = 4;
  bytes value = 5;
  int64 lease = 6;
}

• Key - key in bytes. An empty key is not allowed.
• Value - value in bytes.
• Version - version is the version of the key. A deletion resets the version to zero and any modification of the key increases its version.
• Create_Revision - revision of the last creation on the key.
• Mod_Revision - revision of the last modification on the key.
• Lease - the ID of the lease attached to the key. If lease is 0, then no lease is attached to the key.