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Expose swarmkit's Raft tuning parameters in engine config #36726

merged 1 commit into from Mar 30, 2018



chungers commented Mar 29, 2018

Signed-off-by: David Chung

- What I did
This PR exposes the HeartbeatTick and ElectionTick parameters for Swarmkit's Raft quorum. This allows tuning of the leader election behavior of the Swarm managers. This PR contains default values so these settings are strictly optional. Changing these settings can adjust the sensitivity of Swarm managers to transient events in their environment and make the quorum more stable.

- How I did it
Swarmkit already exposes these parameters but they are previously hardcoded. This PR plumbs these settings through to expose them in the daemon's config.

- How to verify it
Changing the daemon's config JSON should override the default values.

- Description for the changelog

Make Swarm manager Raft quorum parameters configurable in daemon config.

- A picture of a cute animal (not mandatory but encouraged)

David Chung
Expose swarm raft tuning parameters in engine config
Signed-off-by: David Chung <>

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codecov bot commented Mar 29, 2018

Codecov Report

❗️ No coverage uploaded for pull request base (master@18d1688). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master   #36726   +/-   ##
  Coverage          ?    35.2%           
  Files             ?      613           
  Lines             ?    45562           
  Branches          ?        0           
  Hits              ?    16038           
  Misses            ?    27396           
  Partials          ?     2128





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stevvooe commented Mar 29, 2018


1 similar comment

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tonistiigi commented Mar 30, 2018


@tonistiigi tonistiigi merged commit 8b6a827 into moby:master Mar 30, 2018

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thaJeztah commented Mar 30, 2018

Looks like this needs an update in the docs, also;

  • should this be exposed as a flag as well?
  • is this configuration live-reloadable?
if config.RaftElectionTick == 0 {
// 10X heartbeat tick is the recommended ratio according to etcd docs.
config.RaftElectionTick = 10 * config.RaftHeartbeatTick

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thaJeztah Apr 5, 2018


What happens if I configure RaftElectionTick < RaftHeartbeatTick? Should RaftElectionTick always be multiple times RaftHeartbeatTick? If so; should we add validation here, or have a ratio instead as configuration?

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chungers Apr 10, 2018


This here doesn't enforce that RaftElectionTick should always be > than RaftHearbeatTick and should be at least 10 (which is the default value when nothing is set).

I can add a check to return an error when RaftElectionTick is strictly greater than RaftHeartbeatTick and prevent the daemon from starting up. Is this acceptable?

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