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James Turnbull dd4918fd16 Documentation pass 
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docs Commands: Exec docs-commands-exec The exec command provides a mechanism for remote execution. For example, this can be used to run the `uptime` command across all machines providing the `web` service.

Consul Exec

Command: consul exec

The exec command provides a mechanism for remote execution. For example, this can be used to run the uptime command across all machines providing the web service.

Remote execution works by specifying a job, which is stored in the KV store. Agents are informed about the new job using the event system, which propagates messages via the gossip protocol. As a result, delivery is best-effort, and there is no guarantee of execution.

While events are purely gossip driven, remote execution relies on the KV store as a message broker. As a result, the exec command will not be able to properly function during a Consul outage.

Verbose output warning: use care to make sure that your command does not produce a large volume of output. Writes to the KV store for this output go through the Consul servers and the Raft consensus algorithm, so having a large number of nodes in the cluster flow a large amount of data through the KV store could make the cluster unavailable.

Usage

Usage: consul exec [options] [-|command...]

The only required option is a command to execute. This is either given as trailing arguments, or by specifying -; STDIN will be read to completion as a script to evaluate.

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. In version 0.4, that is the only supported value.

  • -prefix - Key prefix in the KV store to use for storing request data. Defaults to _rexec.

  • -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.

  • -wait - Specifies the period of time in which no agent's respond before considering the job finished. This is basically the quiescent time required to assume completion. This period is not a hard deadline, and the command will wait longer depending on various heuristics.

  • -wait-repl - Period to wait after writing the job specification for replication. This is a heuristic value and enables agents to do a stale read of the job. Defaults to 200 msec.

  • -verbose - Enables verbose output.

  • -token - The ACL token to use during requests. This token must have access to the prefix in the KV store as well as exec "write" access for the _rexec event. Defaults to that of the agent.