When changing the index of an Elasticsearch alias via API, do write operations immediately point to the right index after the response?

Question

Let's say I got the alias car-alias pointing to car-index-1. I now want car-alias to point to car-index-2.

I therefore perform the following POST request to the Aliases API:

{
  "actions": [
    {
      "remove": {
        "index": "car-index-1",
        "alias": "car-alias"
      }
    },
    {
      "add": {
        "index": "car-index-2",
        "alias": "car-alias"
      }
    }
  ]
}

I receive the following response:

{
   "acknowledged": true
}

Can I now immediately index data into the car-alias and it ends up in the car-index-2?

Or does the "acknowledged": true response not guarantee that write operations point to the right index immediately?

score 1 · Accepted Answer · answered Jan 17 '22 at 12:21

1

Yes, the alias is changed atomically and will point to car-index-2 immediately when the call returns.

As stated in the documentation "...during the swap, the alias has no downtime and never points to both streams at the same time."

answered Jan 17 '22 at 12:21

Val

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So the `acknowledged` flag does not mean that Elasticsearch just acknowledged the operation, but still maybe has some processing to do until is is completed? – Harold L. Brown Jan 17 '22 at 12:35
1

No, it means it's safe and the writes will go to the new index. – Val Jan 17 '22 at 12:35

score 1 · Answer 2 · answered Jan 17 '22 at 12:28

In addition to @Val's answer:

Since in your case, the alias only points to one index, the "next" index is automatically set as the write index.

From the docs regarding the is_write_index option of the add action:

is_write_index (Optional, Boolean) If true, sets the write index or data stream for the alias.

If an alias points to multiple indices or data streams and is_write_index isn’t set, the alias rejects write requests. If an index alias points to one index and is_write_index isn’t set, the index automatically acts as the write index. [...]

Only the add action supports this parameter.

Note that this is only useful if the alias points to more than one indexes, the one to which the write requests should go, must be configured with `is_write_index: true`, but it doesn't seem to be the case here. — Val, Jan 17 '22 at 12:34

When changing the index of an Elasticsearch alias via API, do write operations immediately point to the right index after the response?

2 Answers2