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Prevent allocating shards to broken nodes #18417

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ywelsch opened this issue May 17, 2016 · 5 comments
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Prevent allocating shards to broken nodes #18417

ywelsch opened this issue May 17, 2016 · 5 comments
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>bug :Distributed Coordination/Allocation All issues relating to the decision making around placing a shard (both master logic & on the nodes) Team:Distributed (Obsolete) Meta label for distributed team (obsolete). Replaced by Distributed Indexing/Coordination.

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@ywelsch
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ywelsch commented May 17, 2016

Allocating shards to a node can fail for various reasons. When an allocation fails, we currently ignore the node for that shard during the next allocation round. However, this means that:

  • subsequent rounds consider the node for allocating the shard again.
  • other shards are still allocated to the node (in particular the balancer tries to put shards on that node with the failed shard as its weight becomes smaller).
    This is particularly bad if the node is permanently broken, leading to a never-ending series of failed allocations. Ultimately this affects the stability of the cluster.
@s1monw
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s1monw commented May 17, 2016

@ywelsch I think we can approach this from multiple directions.

  • we can start bottom up and check that a data-path is writeable before we allocate a shard and skip it if possible (that would help if someone looses a disk and has multiple)
  • we can also has a simple allocation_failed counter on UnassignedInfo to prevent endless allocation of a potentially broken index (metadata / settings / whatever is broken)
  • we might also be able to use a simple counter of failed allocations per node that we can reset once we had a successful one on that node. We can then also have a simple allocation decider that throttles that node or takes it out of the loop entirely once the counter goes beyond a threshold?

I think in all of these cases simplicity wins over complex state... my $0.05

s1monw added a commit to s1monw/elasticsearch that referenced this issue May 19, 2016
@s1monw
Limit retries of failed allocations per index
394b280 
Today if a shard fails during initialization phase due to misconfiguration, broken disks,
missing analyzers, not installed plugins etc. elasticsaerch keeps on trying to initialize
or rather allocate that shard. Yet, in the worst case scenario this ends in an endless
allocation loop. To prevent this loop and all it's sideeffects like spamming log files over
and over again this commit adds an allocation decider that stops allocating a shard that
failed more than N times in a row to allocate. The number or retries can be configured via
`index.allocation.max_retry` and it's default is set to `5`. Once the setting is updated
shards with less failures than the number set per index will be allowed to allocate again.

Internally we maintain a counter on the UnassignedInfo that is reset to `0` once the shards
has been started.

Relates to elastic#18417
@s1monw s1monw mentioned this issue May 19, 2016
Merged
s1monw added a commit that referenced this issue May 20, 2016
@s1monw
Limit retries of failed allocations per index (#18467)
35e7058 
Today if a shard fails during initialization phase due to misconfiguration, broken disks,
missing analyzers, not installed plugins etc. elasticsaerch keeps on trying to initialize
or rather allocate that shard. Yet, in the worst case scenario this ends in an endless
allocation loop. To prevent this loop and all it's sideeffects like spamming log files over
and over again this commit adds an allocation decider that stops allocating a shard that
failed more than N times in a row to allocate. The number or retries can be configured via
`index.allocation.max_retry` and it's default is set to `5`. Once the setting is updated
shards with less failures than the number set per index will be allowed to allocate again.

Internally we maintain a counter on the UnassignedInfo that is reset to `0` once the shards
has been started.

Relates to #18417
@jasontedor jasontedor mentioned this issue Aug 3, 2016
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@abeyad abeyad mentioned this issue Aug 8, 2016
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@clintongormley clintongormley mentioned this issue Aug 31, 2016
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@MorrieAtElastic MorrieAtElastic mentioned this issue Jul 7, 2017
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@gmoskovicz
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@ywelsch @s1monw is there are news on this?

Some OSs would cause the mounted disk to be read-only and if so the entire cluster will have issues with RED shards and not moving shards. Perhaps this could help in that end?

@lcawl lcawl added :Distributed Indexing/Distributed A catch all label for anything in the Distributed Area. Please avoid if you can. and removed :Allocation labels Feb 13, 2018
@DaveCTurner DaveCTurner added the :Distributed Coordination/Allocation All issues relating to the decision making around placing a shard (both master logic & on the nodes) label Mar 15, 2018
@elasticmachine
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Pinging @elastic/es-distributed

@DaveCTurner DaveCTurner removed the :Distributed Indexing/Distributed A catch all label for anything in the Distributed Area. Please avoid if you can. label Mar 15, 2018
@bleskes bleskes mentioned this issue Mar 16, 2018
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@bleskes
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bleskes commented Mar 21, 2018

We have another, non trivial, of instance of this in shard fetching. When it hard fails on a node (rather then succeeding by finding a broking copy) we currently redo the fetching. This is an easy way around networking issue but can be poisonous on disk failures (for example).

@DaveCTurner DaveCTurner mentioned this issue Mar 22, 2019
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@DaveCTurner DaveCTurner mentioned this issue Aug 7, 2019
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@DaveCTurner DaveCTurner mentioned this issue Sep 24, 2019
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@dnhatn dnhatn mentioned this issue Oct 29, 2019
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@rjernst rjernst added the Team:Distributed (Obsolete) Meta label for distributed team (obsolete). Replaced by Distributed Indexing/Coordination. label May 4, 2020
@idegtiarenko
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We would rather remove the broken node from the cluster rather then take an fail allocation(s).

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>bug :Distributed Coordination/Allocation All issues relating to the decision making around placing a shard (both master logic & on the nodes) Team:Distributed (Obsolete) Meta label for distributed team (obsolete). Replaced by Distributed Indexing/Coordination.
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@clintongormley @rjernst @s1monw @bleskes @idegtiarenko @gmoskovicz @ywelsch @DaveCTurner @elasticmachine @lcawl