Hi, I’m just getting started with Docker, so apologies in advance if this seems silly.
I used to self-host multiple services (RSS reader, invoicing software, personal wiki) directly on a VPS using nginx and mariadb. I messed it up recently and am starting again, but this time I took the docker route.
So I’ve set up the invoicing software (InvoiceNinja), and everything is working as I want.
Now that I want to add the other services (ttrss and dokuwiki), should I set up new containers? It feels wasteful.
Instead, if I add additional configs to the existing servers that the InvoiceNinja docker-compose generated (nginx and mysql), I’m worried that an update to Invoiceninja would have a chance of messing up the other setups as well.
It shouldn’t, from my understanding of how docker containers work, but I’m not 100% sure. What would be the best way to proceed?
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So from what i get reading your question, i would recommend reading more about container, compose files and how they work.
To your question, i assume when you are talking about adding to container you are actually referring to compose files (often called ‘stacks’)? Containers are basically almost no computational overhead.
I keep my services in extra compose files. Every service that needs a db gets a extra one. This helps to keep things simple and modular.
I need to upgrade a db from a service? -> i do just that and can leave everything else untouched.
Also, typically compose automatically creates a network where all the containing services of that stack communicate. Separating the compose files help to isolate them a little bit with the default settings.
Aren’t containers the product of compose files? i.e. the compose files spin up containers. I understand the architecture, I’m just not sure about how docker streamlines separate containers running the same process (eg, mysql).
I’m getting some answers saying that it deduplicates, and others saying that it doesn’t. It looks more likely that it’s the former though.
A compose file is just the configuration of one or many containers. The container is downloaded from the chosen registry and pretty much does not get touched.
A compose file ‘composes’ multiple containers together. Thats where the name comes from.
When you run multiple databases then those run parallel. So every database has its own processes. You can even see them on the host system by running something like top or htop. The container images themself can get deduplicated that means that container images that contain the same layer just use the already downloaded files from that layer. A layer is nothing else as multiple files bundled. For example you can choose a ‘ubuntu layer’ for the base of your container image and every container that you want to download using that same layer will just simply use those files on creation time. But that basically does not matter. We are talking about a few 10th or 100th of MB in extreme cases.
But important, thoses files are just shared statically and changing a file in one container does not affect the other. Every container has its own isolated filesystem.
I understand the architecture, I’m just not sure about how docker streamlines separate containers running the same process (eg, mysql).
Quite simple actually. It gives every container its own environment thats to namespacing. Every process thinks (more or less) it is running on its own machine.
There are quite simple docker implementations with just a couple of hundreds lines of code.
This how I do it, not saying it’s the best way, but serves me well :).
For each type of application, 1 docker-compose.yaml. This will have all linked containers in 1 file but all your different applications are seperate !
Every application in it’s respective folder.
- home/user/docker/app1/docker-compose.yml
- home/user/docker/app2/docker-compose.yml
- home/user/docker/app3/docker-compose.yml
Everything is behind an application proxy (traefik in my case) and served with self-signed certificate.
I access all my apps through their domain name on my LAN with wireguard.
Yes this is what I want to do. My question is how docker manages shared processes between these apps (for example, if app1 uses mysql and app2 also uses mysql).
Does it take up the RAM of 2 mysql processes? It seems wasteful if that’s the case, especially since I’m on a low-RAM VPS. I’m getting conflicting answers, so it looks like I’ll have to try it out and see.
Nah, that’s not how it works ! I have over 10 applications and half of them have databases, and that’s the prime objective of containers ! Less resource intensive and easier to deploy on low end machines. If I had to deploy 10 VMs for my 10 applications, my computer would not be able to handle it !
I have no idea how it works underneath, that’s a more technical question on how container engines work. But if you searx it or ask chatGPT (if you use this kind of tool) i’m sure you will find out how it works :).
This is promising, thanks!
Containers are very lightweight. I have no desire to build anything so I always just add another service container to my existing stacks.
That was my impression as well. But since I’m on a low-RAM VPS any overhead in RAM adds up, and I wanted to know how process deduplication works before I get into it.