Execute a remote command across a Consul cluster
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README.md

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NAME

AnyEvent::Consul::Exec - Execute a remote command across a Consul cluster

SYNOPSIS

use AnyEvent;
use AnyEvent::Consul::Exec;

my $cv = AE::cv;

my $e = AnyEvent::Consul::Exec->new(
    
    # command to run
    command => 'uptime',

    # number of seconds target will wait for command, without sending
    # output, before terminating it
    wait => 2,
    
    # called once job is submitted to Consul
    on_submit => sub {
        say "job submitted";
    },
    
    # called as each target node starts to process the job
    # multiple calls, once per node
    on_ack => sub {
        my ($node) = @_;
        say "$node: ack";
    },
    
    # called when a node has output from the job
    # can be called zero or more times per node, as more output
    # becomes available
    on_output => sub {
        my ($node, $output) = @_;
        say "$node: output:";
        say "$node> $_" for split("\n", $output);
    },
    
    # called when the node completes a job
    # multiple calls, one per node
    on_exit => sub {
        my ($node, $rc) = @_;
        say "$node: exit: $rc";
    },
    
    # called once all nodes have reported completion
    # object is unusable past this point
    on_done => sub {
        say "job done";
        $cv->send;
    },
    
    # called if an error occurs anywhere during processing (not command errors)
    # typically called if Consul is unable to service requests
    # object is unusable past this point
    on_error => sub {
        my ($err) = @_;
        say "error: $err";
        $cv->send;
    },
);

# begin execution
$e->start;

$cv->recv;

DESCRIPTION

AnyEvent::Consul::Exec is an interface to Consul's "exec" agent function. This is the same thing you get when you run consul exec.

consul exec is great, but its output is text-based, making it awkward to parse to determine what happened on each node that ran the command. AnyEvent::Consul::Exec replaces the client portion with a library you can use to get info about what is happening on each node as it happens.

As the name implies, it expects to be run inside an AnyEvent event loop.

BASICS

Start off by instantiating a AnyEvent::Consul::Exec object with the command you want to run:

my $e = AnyEvent::Consul::Exec->new(
    command => 'uptime',
);

Then call start to kick it off:

$e->start;

As the AnyEvent event loop progresses, the command will be executed on remote nodes. Output and results of that command on each node will be posted to callbacks you can optionally provide to the constructor.

When calling the constructor, you can include the consul_args option with an arrayref as a value. Anything in that arrayref will be passed as-is to the AnyEvent::Consul constructor. Use this to set the various client options documented in AnyEvent::Consul and Consul.

The wait option will tell the target agent how long to wait, without receiving output, before killing the command. This does the same thing as the -wait option to consul exec.

The node, service and tag each take basic regexes that will be used to match nodes to run the command on. See the corresponding options to consul exec for more info.

The dc option can take the name of the datacenter to run the command in. The exec mechanism is limited to a single datacentre. This option will cause AnyEvent::Consul::Exec to find a Consul agent in the named datacenter and execute the command there (without it, the local node is used).

CALLBACKS

AnyEvent::Consul::Exec will arrange for various callbacks to be called as the command is run on each node and its output and exit code returned. Set this up by passing code refs to the constructor:

  • on_submit

    Called when the command is fully accepted by Consul (ie in the KV store, ready for nodes to find).

  • on_ack($node)

    Called for each node as they notice the command has been entered into the KV store and start running it.

  • on_output($node, $output)

    Called when a command emits some output. May be called multiple times per node, or not at all if the command has no output.

  • on_exit($node, $rc)

    Called when a command completes.

  • on_done

    Called when all remote commands have completed. After this call, the object is no longer useful.

  • on_error($err)

    Called if an error occurs while communicating with Consul (local agent unavailable, quorum loss, etc). After this call, the object is no longer useful.

CAVEATS

Consul's remote execution protocol is internal to Consul itself and is not documented. This module has been confirmed to work in Consul 0.9.0 (the latest release at the time of writing). The Consul authors may change the underlying mechanism in the future, but this module should continue to work.

SUPPORT

Bugs / Feature Requests

Please report any bugs or feature requests through the issue tracker at https://github.com/robn/AnyEvent-Consul-Exec/issues. You will be notified automatically of any progress on your issue.

Source Code

This is open source software. The code repository is available for public review and contribution under the terms of the license.

https://github.com/robn/AnyEvent-Consul-Exec

git clone https://github.com/robn/AnyEvent-Consul-Exec.git

AUTHORS

COPYRIGHT AND LICENSE

This software is copyright (c) 2017 by Rob N ★ and was supported by FastMail Pty Ltd.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.