Can all docker swarm instances run on same machine?

Question

I have a couple of Docker swarm questions (Sorry for not splitting them up but they are all closely related):

• Do all instances in a swarm have to run on different machines or can they all run on the same? (if having limited amount of hardware and just wanting to try swarm mode)
• Do I have to run swarm mode to be able to communicate between instances?
• What is the key difference between swarm mode and just running a number of containers as regular?
• What are the options of communication between instances of containers? (in swarm and in regular mode) http? named pipes? other?
• If using http communication between containers on same machine, will it be roughly similarly as fast as named pipes?
• Is there any built in support for a message bus or similar in Docker?
• Is there support for any consensus protocol in Docker?
• Are there any GUI's for designing, managing, testing and/or debugging Docker swarms?
• Can a container list other containers, stop/restart some and start new ones? (to be able to function as a manager for other containers)
• Can a container be given access to OS-features (Linux in my case) to configure for instance a reverse proxy or port forwarding on the WAN?

Background: What I'm trying to figure out is how I should go about and build a micro service mesh using Docker. The containers will be running .NET Core. I'm not too keen on relying too much on specifically Docker since it may not be the preferred tech in a couple of years. What can/should I do with Docker and what can/should I do inside the containers. That's what I'm trying to figure out.

Answer 1

I've copied your questions and tried to answer them.

• Do all instances in a swarm have to run on different machines or can they all run on the same? (if having limited amount of hardware and just wanting to try swarm mode)
  • You can have only one machine in a swarm and run multiple tasks of the same service or in other words your scale of a service can be more than the number of actual machines. I have a testing swarm with a single machine and one with three and it works the same way.
• Do I have to run swarm mode to be able to communicate between instances?
  • You have to run your docker in swarm mode in order to create a service, please see this link
• What is the key difference between swarm mode and just running a number of containers as regular?
  • The key difference afaik is, that when a task goes down, docker puts another task up automatically. And you can easily scale your services, which means you can easily have multiple tasks just by scaling your service (up or down). As of running a container - when it goes down you have to manually start another.
• What are the options of communication between instances of containers? (in swarm and in regular mode) http? named pipes? other?
  • I've currently only tested with a couple of wildfly servers in a swarm, which are on the same network. I'm not sure about others, but would love to find out. I've only read about RabbitMQ, but can't seem to find the link atm.
• If using http communication between containers on same machine, will it be roughly similarly as fast as named pipes?
  • I can't say.
• Is there any built in support for a message bus or similar in Docker?
  • I can't say.
• Are there any GUI's for designing, managing, testing and/or debugging Docker swarms?
  • I've tested rancher and portainer.io, for a list of them I found this link
• Can a container list other containers, stop/restart some and start new ones?
  • I'm not sure why would you want to do that? And I guess it's possible, see this link
• Can a container be given access to OS-features (Linux in my case) to configure for instance a reverse proxy or port forwarding on the WAN?
  • I can't say.