I was writing an ansible playbook to deploy an Apache Flink cluster, and I ran into this problem while editing the configuration files:
How can I get the total number of the vCPUs of all the “slave” machines running on the cluster?
I thought of the hostvars ansible variable, which stores the gathered facts about the hosts, so using the debug module, I printed it out. The result was a JSON like that:
{
"node1": {"flink_type": "master", "ansible_processor_vcpus": 2, ...},
"node2": {"flink_type": "slave", "ansible_processor_vcpus": 4, ...},
"node3": {"flink_type": "slave", "ansible_processor_vcpus": 8, ...}
}
So all I needed to do was to filter the nodes on the value of the attribute flink_type and get a list of their ansible_processor_vcpus values, so that I can then sum them up with jinja, right?
Well it wasn’t very easy. As it turns out, if my case was:
{
"nodes": [
{"flink_type": "master", "ansible_processor_vcpus": 2, ...},
{"flink_type": "slave", "ansible_processor_vcpus": 4, ...},
{"flink_type": "slave", "ansible_processor_vcpus": 8, ...}
]
}
the query-solution would be as easy as nodes[?flink_type=='slave'].ansible_processor_vcpus, which would return the list [4, 8].
But in my case, I first needed to convert the JSON into a list of objects, then get the first element of this list, and then perform the filtering and attribute selection.
The solution I have found to be working correctly is this one:
[@.*][0][?flink_type==`slave`].ansible_processor_vcpus
, which is very ugly. I was hoping I could do something like *[?flink_type=='slave'].ansible_processor_vcpus but this doesn’t work.
If there is a more elegant solution to this, I would really like to hear it, contact links are below.