Accessing services on the Docker host

[joho68]

I’ve tried to find the answer to this in so many places, and gotten so many different suggestions and replies, so let’s go for the Jackpot and ask here

What I’d like to do is to setup two Docker containers (in this case Synapse) on the same VPS. On that VPS, things like database, MTA (Postfix), and other nice things are already running. I don’t want to duplicate these inside each container; part due to maintenance, part due to resources.

But it seems near impossible (for me) to get this working smoothly. So I’m either doing something wrong, or it’s not doable (which doesn’t sound right to me).

Can someone explain to me if this a) is possible, and if so, b) possibly point me in the right direction as far as Docker networking is concerned, which I’m guessing is issue at hand here.

I’m using this https://hub.docker.com/r/matrixdotorg/synapse as per the official documentation.

-joho

[meyay (Metin Y.)]

Can you share what you found out, and what you tried, so we can see if it just needs a tiny nudge to get things up and running?

[rimelek (Ákos Takács)]

You can access services on the host by using the host IP as you would on any server. Or if you want to access services listening on a loopback IP only

Host.docker.internal in production environment

Once again a question that inspired me to try something. Actually I have been thinking for a while about trying to implement a feature like the one in Docker desktop that lets you use host.docker.internal to connect to the localhost of the host machine. I think I have done it. So host.docker.internal is not just a hostname that directly points to the IP address of your host. It will point to the “host gateway” which can be configured but it is 172.17.0.1 by default which is the gateway of the d…

But we had another (I believe) similar topic where @meyay explained what the recommended solution would be. You don’t need t duplicate, especially not in every container since every container should run a single main process which can create more.But in the long term, you can try to run the other services in containers too. Depending on those services of course.

Unable to access host's localhost from container

I missed a crucial detail: I seem to have skipped the first line and assumed mysql is running on the host. Why would you want to use the published host port to access the database from another container? The intended approach is to put the app container and database container in the same user defined network, then use dns-based service discovery to communicate from the app container to the database container. The networks internal dns, will resolve the service name (docker compose only), cont…