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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.

The table below shows the required ACLs in order to execute this command.

ACL RequiredScope
agent:readlocal agent
session:writelocal agent
key:write"_rexec" prefix
event:write"_rexec" prefix

In addition to the above, the policy associated with the agent token should have write on "_rexec" key prefix. This policy permits agents to read the exec command and write its output back to the KV store.

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.

Command Options

  • -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.

  • -shell - Optional, use a shell to run the command. The default value is true.

  • -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.

API Options

  • -ca-file=<value> - Path to a CA file to use for TLS when communicating with Consul. This can also be specified via the CONSUL_CACERT environment variable.

  • -ca-path=<value> - Path to a directory of CA certificates to use for TLS when communicating with Consul. This can also be specified via the CONSUL_CAPATH environment variable.

  • -client-cert=<value> - Path to a client cert file to use for TLS when verify_incoming is enabled. This can also be specified via the CONSUL_CLIENT_CERT environment variable.

  • -client-key=<value> - Path to a client key file to use for TLS when verify_incoming is enabled. This can also be specified via the CONSUL_CLIENT_KEY environment variable.

  • -http-addr=<addr> - Address of the Consul agent with the port. This can be an IP address or DNS address, but it must include the port. This can also be specified via the CONSUL_HTTP_ADDR environment variable. In Consul 0.8 and later, the default value is http://127.0.0.1:8500, and https can optionally be used instead. The scheme can also be set to HTTPS by setting the environment variable CONSUL_HTTP_SSL=true. This may be a unix domain socket using unix:///path/to/socket if the agent is configured to listen that way.

  • -tls-server-name=<value> - The server name to use as the SNI host when connecting via TLS. This can also be specified via the CONSUL_TLS_SERVER_NAME environment variable.

  • -token=<value> - ACL token to use in the request. This can also be specified via the CONSUL_HTTP_TOKEN environment variable. If unspecified, the query will default to the token of the Consul agent at the HTTP address.

  • -token-file=<value> - File containing the ACL token to use in the request instead of one specified via the -token argument or CONSUL_HTTP_TOKEN environment variable. This can also be specified via the CONSUL_HTTP_TOKEN_FILE environment variable.

  • -datacenter=<name> - Name of the datacenter to query. If unspecified, the query will default to the datacenter of the Consul agent at the HTTP address.

  • -stale - Permit any Consul server (non-leader) to respond to this request. This allows for lower latency and higher throughput, but can result in stale data. This option has no effect on non-read operations. The default value is false.