Cameron Stokes af1d22135a [docs] Autopilot guide: clarify left status

2017-04-10 11:18:54 -07:00

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layout	page_title	sidebar_current	description
docs	Autopilot	docs-guides-autopilot	This guide covers how to configure and use Autopilot features.

Autopilot

Autopilot is a set of new features added in Consul 0.8 to allow for automatic operator-friendly management of Consul servers. It includes cleanup of dead servers, monitoring the state of the Raft cluster, and stable server introduction.

To enable Autopilot features (with the exception of dead server cleanup), the raft_protocol setting in the Agent configuration must be set to 3 or higher on all servers. In Consul 0.8 this setting defaults to 2; in Consul 0.9 it will default to 3. For more information, see the Version Upgrade section on Raft Protocol versions.

Configuration

The configuration of Autopilot is loaded by the leader from the agent's autopilot settings when initially bootstrapping the cluster. After bootstrapping, the configuration can be viewed or modified either via the [operator autopilot] (/docs/commands/operator/autopilot.html) subcommand or the /v1/operator/autopilot/configuration HTTP endpoint:

$ consul operator autopilot get-config
CleanupDeadServers = true
LastContactThreshold = 200ms
MaxTrailingLogs = 250
ServerStabilizationTime = 10s
RedundancyZoneTag = ""
DisableUpgradeMigration = false

$ consul operator autopilot set-config -cleanup-dead-servers=false
Configuration updated!

$ consul operator autopilot get-config
CleanupDeadServers = false
LastContactThreshold = 200ms
MaxTrailingLogs = 250
ServerStabilizationTime = 10s
RedundancyZoneTag = ""
DisableUpgradeMigration = false

Dead Server Cleanup

Dead servers will periodically be cleaned up and removed from the Raft peer set, to prevent them from interfering with the quorum size and leader elections. This cleanup will also happen whenever a new server is successfully added to the cluster.

Prior to Autopilot, it would take 72 hours for dead servers to be automatically reaped, or operators had to script a consul force-leave. If another server failure occurred, it could jeopardize the quorum, even if the failed Consul server had been automatically replaced. Autopilot helps prevent these kinds of outages by quickly removing failed servers as soon as a replacement Consul server comes online. When servers are removed by the cleanup process they will enter the "left" state.

This option can be disabled by running consul operator autopilot set-config with the -cleanup-dead-servers=false option.

Server Health Checking

An internal health check runs on the leader to track the stability of servers.
A server is considered healthy if:

It has a SerfHealth status of 'Alive'
The time since its last contact with the current leader is below LastContactThreshold
Its latest Raft term matches the leader's term
The number of Raft log entries it trails the leader by does not exceed MaxTrailingLogs

The status of these health checks can be viewed through the [/v1/operator/autopilot/health] (/api/operator.html#autopilot-health) HTTP endpoint, with a top level Healthy field indicating the overall status of the cluster:

$ curl localhost:8500/v1/operator/autopilot/health
{
    "Healthy": true,
    "FailureTolerance": 0,
    "Servers": [
        {
            "ID": "e349749b-3303-3ddf-959c-b5885a0e1f6e",
            "Name": "node1",
            "Address": "127.0.0.1:8300",
            "SerfStatus": "alive",
            "Version": "0.8.0",
            "Leader": true,
            "LastContact": "0s",
            "LastTerm": 2,
            "LastIndex": 10,
            "Healthy": true,
            "Voter": true,
            "StableSince": "2017-03-28T18:28:52Z"
        },
        {
            "ID": "e35bde83-4e9c-434f-a6ef-453f44ee21ea",
            "Name": "node2",
            "Address": "127.0.0.1:8705",
            "SerfStatus": "alive",
            "Version": "0.8.0",
            "Leader": false,
            "LastContact": "35.371007ms",
            "LastTerm": 2,
            "LastIndex": 10,
            "Healthy": true,
            "Voter": false,
            "StableSince": "2017-03-28T18:29:10Z"
        }
    ]
}

Stable Server Introduction

When a new server is added to the cluster, there is a waiting period where it must be healthy and stable for a certain amount of time before being promoted to a full, voting member. This can be configured via the ServerStabilizationTime setting.

~> The following Autopilot features are available only in Consul Enterprise version 0.8.0 and later.

Server Read Scaling

With the -non-voting-server option, a server can be explicitly marked as a non-voter and will never be promoted to a voting member. This can be useful when more read scaling is needed; being a non-voter means that the server will still have data replicated to it, but it will not be part of the quorum that the leader must wait for before committing log entries.

Redundancy Zones

Prior to Autopilot, it was difficult to deploy servers in a way that took advantage of isolated failure domains such as AWS Availability Zones; users would be forced to either have an overly-large quorum (2-3 nodes per AZ) or give up redundancy within an AZ by deploying just one server in each.

If the RedundancyZoneTag setting is set, Consul will use its value to look for a zone in each server's specified -node-meta tag. For example, if RedundancyZoneTag is set to zone, and -node-meta zone:east1a is used when starting a server, that server's redundancy zone will be east1a.

Consul will then use these values to partition the servers by redundancy zone, and will aim to keep one voting server per zone. Extra servers in each zone will stay as non-voters on standby to be promoted if the active voter leaves or dies.

Upgrade Migrations

Autopilot in Consul Enterprise supports upgrade migrations by default. To disable this functionality, set DisableUpgradeMigration to true.

When a new server is added and Autopilot detects that its Consul version is newer than that of the existing servers, Autopilot will avoid promoting the new server until enough newer-versioned servers have been added to the cluster. When the count of new servers equals or exceeds that of the old servers, Autopilot will begin promoting the new servers to voters and demoting the old servers. After this is finished, the old servers can be safely removed from the cluster.

To check the consul version of the servers, either the [autopilot health] (/api/operator.html#autopilot-health) endpoint or the consul members command can be used:

$ consul members
Node   Address         Status  Type    Build  Protocol  DC
node1  127.0.0.1:8301  alive   server  0.7.5  2         dc1
node2  127.0.0.1:8703  alive   server  0.7.5  2         dc1
node3  127.0.0.1:8803  alive   server  0.7.5  2         dc1
node4  127.0.0.1:8203  alive   server  0.8.0  2         dc1

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