Abitrary JSON Query/Evaluation (Nagios Plugin)

Many modern apps in the web stack have JSON interfaces.

We needed highly-customizable way to add JSON checks to Nagios. We needed more than simple foo.bar.baz == 'zerp' checks. We found ourselves wanting to write simple JavaScript to evaluate API responses. jsoneval allows this.

Here are a couple examples.

Check ElasticSearch cluster health

define command{
    command_name    check_es_cluster_health
    command_line    /opt/node/bin/node /usr/lib/nagios/plugins/nagios-jsoneval/jsoneval.js -u http://$HOSTADDRESS$:$ARG1$/_cluster/health -e 'json.status' -t 'green'
}

define service {
    use                     generic-service
    hostgroup_name          elasticsearch-servers
    service_description     ElasticSearch Cluster Health
    check_command           check_es_cluster_health!9200
}

This will trigger critical status if your cluster is yellow or red (not green).

Check RabbitMQ queue length

First, you'll need the RabbitMQ Management Plugin enabled, and a user with appropriate permissions.

define host{
    name servicenode-template
    register 0
    use generic-host
    hostgroups generic-hosts, rabbitmq-servers
    _rabbitmq_user monitor
    _rabbitmq_pass monitor
}

define host{
    use servicenode-template
    host_name svc01
    address svc01.exmaple.com
}

define command{
    command_name    check_rabbitmq_queue_length
    command_line    /opt/node/bin/node /usr/lib/nagios/plugins/nagios-jsoneval/jsoneval.js -u http://$_HOSTRABBITMQ_USER$:$_HOSTRABBITMQ_PASS$@$HOSTADDRESS$:55672/api/queues -e 'json.forEach(function (q) {if (q.vhost == "$ARG1$" && q.name == "$ARG2$") { retval = q.messages }})' -c $ARG3$ -w $ARG4$
}

define service {
    use                     generic-service
    hostgroup_name          rabbitmq-servers
    service_description     RabbitMQ gimmebar:dropbox-worker queue length
    check_command           check_rabbitmq_queue_length!/gimmebar!dropbox-worker!100!25
}

This checks the dropbox-worker queue in the /gimmebar vhost. A warning will be triggered at a queue length of 25, and a critical at 100.

Note that we've put the user and password into custom host variables, but they could also be loaded into your resources file and referenced as $USER{N}$.

Be careful with semi-colons (;) in Nagios commands. See the note about command_line.