What benefits does Docker Compose have over Docker

Question

From what I read it seems that Docker-Compose is a tool to create multiple containers on a single host while Docker Swarm is a tool that can do the exact same thing but with more control and on multiple hosts with the help of Docker Stack. I went through the tutorial and also came across this thread:

docker-compose.yml vs docker-stack.yml what difference?

And I'm coming to the conclusion that there's no reason to ever use Docker-Compose when you can use Docker Swarm with Docker Stack. They can even use the same docker-compose.yml.

It seems that Docker-compose came before the swarm and stack and maybe the new solution of swarm + stack makes compose obsolete, but it still remains for legacy reasons. Is this thinking correct? If not, what benefits does Docker-Compose have over Docker Swarm and Docker Stack in terms of making a development or production environment?

Answer 1

From what I have found: What's the difference between Docker Swarm, Docker Compose and Docker Networks?

Docker Compose is a client side tool that allows you to run an application stack with multiple components.

So in our scenario you would use Docker Compose to achieve - #2*¹. You will define a spec file where you would define how a container has to built for each of your components - db, app and web tier. You can also specify how will those interact with each other. How many instance of each and many other things.

*¹ Now you have a requirement to start an application stack which has web tier, app tier and db tier.

---

Compose is a tool for defining and running multi-container Docker applications.

Docker Swarm is a server side feature that enables you to:

• A swarm is a cluster of docker nodes (machines) that act as underlying resources for starting multiple container. One can orchestrate and deploy services across the swarm.

  You can combine multiple nodes as a cluster and then send “docker run” command to this cluster (actually to the Swarm manager node) Swarm will handle scheduling(starting) this container on one of the nodes.

• Allow containers across all nodes to communicate with one another

View official documentation at: Swarm mode overview & Docker Compose

Answer 2

It seems that Docker-compose came before the swarm and stack and maybe the new solution of swarm + stack makes compose obsolete, but it still remains for legacy reasons. Is this thinking correct?

In short, yes. Compose came before all the Swarm stuff (it originated as a 3rd party utility called fig). To make matters worse, there are even two different Swarms, old Swarm (the one that was a separate tool) and Swarm Mode (which is built into the docker binary these days).

It seems to be evolving into services and deployment concepts that get built into Docker. But I would guess Docker Compose and the Swarm Mode deployment stuff will live side by side for a while.

It is also beneficial to know that Docker Compose underpinnings live as a library called libcompose (https://github.com/docker/libcompose) which other 3rd party utilities make use of to support the docker-compose.yml file format for deploying (see Rancher and rancher-compose as an example). I would imagine they would make an effort to continue support for libcompose.

I am unclear if the Docker Swarm deployment stuff actually uses libcompose. In my cursory searches, it would appear that Swarm Mode does not implement libcompose and does its own thing. I am not sure how this relates to the future of Docker Compose and libcompose. Interpret as you see fit...