The question title is the specific problem I am trying to solve. But even more simply, is it at all possible to list all tasks in a service together with the node IPs running them?
docker service ps will list task IDs together with the hostname of the node the task is running on. No other node identifier is provided such as ID or IP.
But I am using Vagrant to manage VMs and without a hostname configured, all host names are named the same ("vagrant"). This makes it very hard for me to figure out exactly which node is running the task!
This is important because I have to manually delete unused images or risk having the machines crash in the future when there's no more disk space. So figuring out where a task ran is the first step of this process lol.
For you Vagrant users, I changed my hostname quite easily in the Vagrantfile using the config.vm.hostname option. But of course, the question is still totally legit.
I can manually run docker images or docker ps on each node to figure out which node store the expected image and/or is currently running which container (the container name would be a concatenation of the task ID and task name, separated with a dot). But this is cumbersome.
I could also list all nodes with their IDs using docker node ls and then headhunt the task for each node, for example by using docker node ps 7b ("7b" is the first two letters in one of my node IDs). But this is cumbersome too and at best, I will "only" learn the node ID and not the IP.
But, I can find the IP using a node ID with a command like this: docker inspect 7b --format '{{.Status.Addr}}'. So getting at the IP directly is not a strict requirement and for a moment - when I understood this - I thought finding a node ID for a given task ID is going to be much easier!
But no. Even this seems to be impossible? As noted earlier, docker service ps does not give me the node ID. The docs for the command says that the placeholder .Name should give me the "Node ID" but this is wrong.
Until this moment I must have tried a billion different hacks.
One thing in particular that I find disturbing is that the docs for the docker node ps command explicitly states that it can be used to "list tasks running on one or more nodes" (emphasize mine). But if I do this: docker node ps vagrant I get an error message that the hostname is ambiguous because it resolves to more than one node! lol isn't that funny (even without using hostnames I have not gotten this command to work for listing tasks on multiple nodes). Not that it matters, because docker node ps just like docker service ps does not even output node IDs and the docs for both these commands lie about being able to do so.
So there you have it. I am left wondering if there's something right in front of me that I have missed or is the entire world relying on unique hostnames? It feels like I have to miss something obvious. Surely this oh so popular product Docker must be able to provide a way to find a node ID or node IP given a task ID? hmm.
I am running Docker version 17.06.2.
This gives me the node ID, given a <task ID>:
docker inspect <task ID> --format '{{.NodeID}}'
Use the node ID to get the node IP:
docker inspect <node ID> --format '{{.Status.Addr}}'
Or, all in one compressed line:
docker inspect -f '{{.Status.Addr}}' $(docker inspect -f '{{.NodeID}}' <task ID>)
As a bonus, the MAC address:
docker inspect -f '{{.NetworkSettings.Networks.ingress.MacAddress}}' $(docker inspect -f '{{.Status.ContainerStatus.ContainerID}}' <task ID>)