index / events API

[schmichael]

When debugging application interactions with etcd it's often useful to view events in index order instead of as a hierarchical tree of keys. Currently this history can be constructed through a sequence of watches which increment the waitIndex over the desired window.

For example if I want to know what happened between indexes 20 and 30:

http localhost:4001/v2/keys/ recursive==true waitIndex==20
http localhost:4001/v2/keys/ recursive==true waitIndex==21
http localhost:4001/v2/keys/ recursive==true waitIndex==22
...etc...
http localhost:4001/v2/keys/ recursive==true waitIndex==30

A new API to view a history for a given window could simplify this:

http localhost:4001/v2/index/ start==20 end==30

{
    "events": [
        {"index": 20, "action": ..., "node": ...},
        {"index": 21, "action": ..., "node": ...},
        ...
    ]
}

If the requested range is partially outside of etcd's window it would reply with all available events.

If the requested range is completely outside of etcd's window it would reply with a 401 error code like watches.

[xiang90]

Can you please take a look at the v3 api design? I think I have covered what you want there.

v2 API is kind of feature freeze.

[xiang90]

I pasted it here for you

message WatchRequest {
  optional bytes key = 1;
  optional bytes end_key = 2;
  // including
  optional int64 start_index = 3;
  // excluding
  optional int64 end_index = 4;
}

You can simply range over all the key space. And it will return you events in index order.

[kelseyhightower]

@schmichael Thanks for the feedback here. As @xiang90 mentioned this is the direction we plan to take etcd in via the proposed v3 api.

[schmichael]

Looking at #2675 it looks like WatchRequests will work for this case perfectly. I'll close this issue.