I was trying to make a full, consistent backup before an upgrade. Snapshots are at a moment of time, which doesn't work if clients are still updating your indexes.

I tried putting the cluster into read_only mode by setting cluster.blocks.read_only: true, but running a snapshot returned this error:

{"error":"ClusterBlockException[blocked by: [FORBIDDEN/6/cluster read-only (api)];]","status":403}

Please consider allowing snapshots to provide a consistent backup by running when in read-only mode.