query in PromQL to get docker swarm node names instead of node id

PromQL-docker-swarm-node-name.md

PromQL

Prometheus is a time-series db, it's query language called PromQL.

Here are some analogies from SQL which may help to understand the basics of PromQL better:

• metric ~ sql table
• label ~ sql column

example:

• Count how many containers running on each node:

  count(container_last_seen) BY (container_label_com_docker_swarm_node_id)

  the equivalent SQL would be:

    SELECT container_label_com_docker_swarm_node_id, COUNT(container_label_com_docker_swarm_node_id)
    FROM container_last_seen
    GROUP BY container_label_com_docker_swarm_node_id

  the result of this query will be table where each row is a unique container_label_com_docker_swarm_node_id and the value is the number of containers which run on this swarm node.

  To get the corresponding node name as a label, we can use the following query:

    count(container_last_seen) BY (container_label_com_docker_swarm_node_id) * ON (container_label_com_docker_swarm_node_id) GROUP_LEFT(node_name) node_meta 

  the equivalent SQL would be:

    SELECT container_label_com_docker_swarm_node_id, node_name, COUNT(container_label_com_docker_swarm_node_id)
    FROM container_last_seen LEFT JOIN node_meta ON container_label_com_docker_swarm_node_id
    GROUP BY container_label_com_docker_swarm_node_id
  

  let's break this down:

  • ON - join on specific label
  • GROUP_LEFT ~ SQL's LEFT JOIN
  • node_meta - metric which has both container_label_com_docker_swarm_node_id and node_name labels