Elastic shards and replica

Hello everyone,

I would like to understand something about shards and replica,
I have a cluster of 3 DATA nodes (2 Hot and 1 Warm), I have configured ILM to have one shard and one replica in the HOT nodes, and then once it passed to the WARM node, I delete the replica and just save the shards in that node.

Today when I restarted one of my HOT nodes, the stat of some of shards in the WARM nodes became YELLOW

I would like to understand why these shards have been affected as they are in the WARM node and not in the Hot nodes ?

wehn I run GET _cluster/allocation/explain?pretty I get some output like these :

"allocate_explanation" : "cannot allocate because allocation is not permitted to any of the nodes",
"explanation" : "index has a preference for tiers [data_warm,data_hot] and node does not meet the required [data_warm] tier"
"explanation" : "index has a preference for tiers [data_warm,data_hot] and node does not meet the required [data_warm] tier"

"explanation" : "a copy of this shard is already allocated to this node [[metricbeat-7.10.1-2021.03.19-000003][0], node[nN9JxEJrTQ6wIBoQLHC-WA], [P], s[STARTED], a[id=MEt6XzEhS1G2WH6n-2-1jg]]"

Thanks for your help

UPDATE: I restarted all the nodes again, and now the cluster health is GREEN
But It would be cool if someone can explain to me why the shards in the WARM node had been affected when I restarted the HOT node !

Thanks :slight_smile:

The allocation explain output indicates that you did not delete the replica on this index even though it was supposed to be in the warm phase.

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Here is how I Configured ILM:

This should delete all the replicas in the Warm phase, isn't it ?

Looks like it should, but apparently it didn't have that effect. Are you sure this policy applies to the index that caused you trouble?

I have configured all my policies the same way.
I will investigate more to find out if there is something wrong in the cluster, and then I will restartd one hot node, to see if I will get the same result as the first time

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