Using JMESPath, how to filter Consul services which have at least one label defined?

Question

I have a list of services defined in my Consul catalog, and I would like to remove the ones that have no label defined.

This list of services looks like this:

{
    "json": {
        "consul": [],
        "consul-exporter": [],
        "consul-8600": [
            "traefik.enable=false",
            "udp"
        ],
        "snmp-gateway": [],
    }
}

I would like to filter it using JMESPath to have the result containing only

{
    "json": {
        "consul-8600": [
            "traefik.enable=false",
            "udp"
        ],
    }
}

But the syntax of JMESPath filtering remains obscure to me.

I think I should use the length function to get the size of the attributes array, but how?

So far, I have a json.[length(*)>0] filter, but it shows no value.

What should I change to have a non-null result?

Answer 1

I don't think this is possible with JMESPath (at least not in an easy way). ^{See the other answer.}

On the other hand, it is trivial to write your own filter in Python (filter_plugins/myfilters.py):

class FilterModule(object):
    def filters(self):
        return {
            'remove_keys_with_empty_values': self.remove_keys_with_empty_values
        }

    def remove_keys_with_empty_values(self, mydict):
        newdict = dict((key, value) for key, value in mydict.iteritems() if value)
        return newdict

and use it in the playbook:

- debug:
    msg: "{{ json | remove_keys_with_empty_values }}"

Answer 2

^{In Ansible 2.5 and later:}

It is possible by combining JMESPath query with Ansible dict2items filter and Jinja2 dict function:

- debug:
    msg: "{{ dict(json | dict2items | json_query('@[?value].[key, value]')) }}"