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James Turnbull dd4918fd16 Documentation pass 
I was reviewing some docs and found a few issues.

1. Fixed some spelling mistakes.
2. Re-formatted some paragraphs.
3. Changed some potentially loaded language.
4. Fixed some grammar issues.
5. Tried to consistently use syntax-highlighting.
6. Fixed post-period spacing.
7. Fixed some formatting issues and inconsistency.
8. All "notes" are either proper notes or re-written.
2016-11-25 12:02:32 -05:00

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docs Commands: Event docs-commands-event The event command provides a mechanism to fire a custom user event to an entire datacenter. These events are opaque to Consul, but they can be used to build scripting infrastructure to do automated deploys, restart services, or perform any other orchestration action. Events can be handled by using a watch.

Consul Event

Command: consul event

The event command provides a mechanism to fire a custom user event to an entire datacenter. These events are opaque to Consul, but they can be used to build scripting infrastructure to do automated deploys, restart services, or perform any other orchestration action. Events can be handled by using a watch.

Under the hood, events are propagated using the gossip protocol.

While the details are not important for using events, an understanding of the semantics is useful. The gossip layer will make a best-effort to deliver the event, but there is no guaranteed delivery. Unlike most Consul data, which is replicated using consensus, event data is purely peer-to-peer over gossip. This means it is not persisted and does not have a total ordering. In practice, this means you cannot rely on the order of message delivery. An advantage however is that events can still be used even in the absence of server nodes or during an outage.

The underlying gossip also sets limits on the size of a user event message. It is hard to give an exact number, as it depends on various parameters of the event, but the payload should be kept very small (< 100 bytes). Specifying too large of an event will return an error.

Usage

Usage: consul event [options] [payload]

The only required option is -name which specifies the event name. An optional payload can be provided as the final argument.

The list of available flags are:

  • -http-addr - Address to the HTTP server of the agent you want to contact to send this command. If this isn't specified, the command will contact 127.0.0.1:8500 which is the default HTTP address of a Consul agent.

  • -datacenter - Datacenter to query. Defaults to that of agent.

  • -name - The name of the event.

  • -node - Regular expression to filter nodes which should evaluate the event.

  • -service - Regular expression to filter to only nodes with matching services.

  • -tag - Regular expression to filter to only nodes with a service that has a matching tag. This must be used with -service. As an example, you may do -service mysql -tag secondary.

  • -token - The ACL token to use when firing the event. This token must have write-level privileges for the event specified. Defaults to that of the agent.