I have a 2 machine swarm cluster. I have installed the simple Docker compose demo from here on one of the machines. However, when I try to scale the application with the docker-compose scale web=5command, it only scales to the current machine and does not create any of the new web containers on the other machine in the swarm cluster as expected.
On every example I've seen by others, their scale command just works and nothing was mentioned about additional configurations needed get it to scale across multiple nodes.
Not sure what else to try. I get the same result when running the scale command from either machine
Please let me know what further information I can provide.
I see now there were two issues causing my scale commands to fail, however, it is still not working even with proper multi-host networking setup.
When scaling a container from a compose application that was linked to another container in that same compose app - This was failing because I was joining the containers with the deprecated(?) "links" functionality rather than using the new multi-host networking functionality. Apparently, "links" can only work on a single machine and cannot be scaled across multiple machines. (I'm fairly sure this is the case, but could be wrong)
When attempting to scale an unlinked container - This was actually working as expected. I had forgot I had other containers running on the machine I was expecting Docker to scale out my container to. Thus the Swarm scheduler just put the newly scaled containers onto the current machine since the current machine was being least utilized. (This was on a 2 machine swarm cluster)
EDIT - Actual Solution
Okay, it looks like the final problem was I cannot scale the part of the compose app that uses build for creating its image rather than specifying the image with image.
I suppose this makes sense because the machine it is trying to scale that container to doesn't have the build file available to create that image but I had assumed Docker Compose/Swarm would be smart enough to figure that out and somehow copy that across machines.
So the solution is to build that image beforehand with Docker build and then either push that image to the public Docker Hub or your own private registry and have the Docker compose file specify that image with image rather than trying to create it with build.