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| docs | Commands: Event | docs-commands-event |
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 propogated 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 guarantee 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 absense 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 which 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 "-server mysql -tag slave".