Container Manager (Docker) Basics on Synology

What Containers and Docker Are

Let us skip the jargon and use a kitchen. Imagine each app on your NAS is a meal. Normally, you cook every meal in the same kitchen, sharing the same pots and counters. If one recipe makes a mess, it can spoil the others.

A container is like packing each meal into its own sealed lunchbox, with its own little set of everything it needs. The apps do not share pots or bump into each other. If one lunchbox spills, the others are untouched. That neat separation is the whole point.

Container Manager Is the DSM 7.2 Name

If you have read older guides online, you may have seen the word "Docker" used as the name of a Synology app. That name has changed, and it is worth knowing why so you are not confused.

In DSM 7.2, Synology renamed its Docker package to Container Manager. It is the same idea and does the same job - running containers - just with a friendlier name and a refreshed look. So when an old tutorial says "open Docker on your Synology," the modern equivalent is "open Container Manager."

• Container Manager and the old Docker package are the same tool, renamed.
• Online guides written before the change will say Docker - that is fine.
• Container Manager also added support for Projects, which we cover later.

Does Your Model Support It?

Here is an important reality check before you go any further: not every Synology can run Container Manager. It is worth confirming yours can, so you do not spend time chasing something your model cannot do.

Container Manager tends to be available on the more capable NAS models - typically the ones with stronger processors and more memory. Smaller, entry-level models, and some models built for light home use, may not support it at all. Synology lists which models are compatible.

• Open Package Center and search for Container Manager - if it does not appear, your model may not support it.
• Check Synology's website, which lists the models that support Container Manager.
• Note that containers also want a decent amount of memory to run comfortably.

Installing Container Manager

If your model supports it, installing is the easy part. It is the same simple process as any other Synology package.

When it opens, you will see areas for things like Image, Container, Registry, and Project. Do not feel you must understand all of them at once - the next chapters walk through the ones that matter, one at a time.

• Make sure your DSM is up to date first, ideally DSM 7.2 or newer.
• Open Package Center in DSM.
• Search for Container Manager.
• Click Install and wait for it to finish.
• Open Container Manager from the main menu when it is ready.

The Registry - Where Images Come From

To run a container, you first need an image. An image is the recipe and ingredients for an app, all packaged up. The registry is the online library where these images are stored and downloaded from.

Think of the registry as a huge cookbook shelf on the internet. You search it, find the app you want, and download its image to your NAS. The best-known registry is called Docker Hub, and Container Manager can search it for you right inside the app.

Running a Simple Container

Let us walk through the shape of running one container. We will keep it general, because every app is a little different, but the steps rhyme every time.

Once it is running, the Container area shows it with a little status light. From there you can start it, stop it, or open its settings. Do not rush the settings screens - ports and volumes, coming up next, are where you make it behave the way you want.

• In Container Manager, go to the Registry area.
• Search for the app you want, and pick the official image.
• Download the image to your NAS.
• Go to the Image area and choose to run the downloaded image.
• Step through the settings - name, ports, volumes - which we explain next.
• Finish, and the container starts up in the Container area.

Ports Explained Simply

When a container has a web page or service you visit, you reach it through a port. A port is just a numbered door on your NAS. Different apps use different door numbers so they do not collide.

Picture your NAS as a building with many numbered doors. When you set up a container, you choose which door number on the NAS leads into that app. Then you visit the app by typing your NAS's address followed by that door number, like adding :8080 on the end.

• Two apps cannot use the same door number at the same time - pick a free number for each.
• Container Manager will often suggest a free port, which is the easy path.
• Write down which port belongs to which app so you remember later.

Volumes - Making Your Data Survive

This is the chapter that saves your data, so read it twice. By default, whatever a container creates lives inside its own sealed lunchbox - and if you remove the container, that data goes with it. A volume fixes that.

A volume connects a folder inside the container to a real folder on your NAS. Now the app writes its important files into your NAS folder instead of the disposable lunchbox. Remove or rebuild the container later, and your data is safe and sound in the NAS folder, ready to be reconnected.

• First make a shared folder on your NAS to hold the app's data, with a clear name.
• In the container's settings, find the Volume section.
• Map your NAS folder to the folder the app expects inside the container.
• The app's guide usually tells you which inside folder it wants mapped.

Environment Variables in Brief

Some containers ask you to fill in a few environment variables. Despite the intimidating name, these are just settings you hand the app when it starts - like filling in a short form before the app runs.

Each one is a name and a value. An app might ask for your time zone, a username, or a starting password. You type the value it wants next to the name it lists. The app's own instructions tell you which ones it expects and what to put.

• They appear as a list of blanks in the container's setup screen.
• Only fill in the ones the app's guide actually asks for.
• Treat any that set a password with care - choose a strong one.

Projects - For Multi-Part Apps

Some apps are not a single container but several that work together - say, one for the app and one for its database. Setting those up by hand, one at a time, is fiddly. Projects solve this.

A Project uses a single recipe file, traditionally called a docker-compose file, that describes all the containers and their settings in one place. Container Manager reads that one file and sets up the whole group correctly. It is like handing the kitchen a full menu instead of ordering each dish separately.

• When an app's instructions give you a block of compose text to paste in.
• When an app clearly needs more than one container to work.
• In Container Manager, you create a Project and provide that compose file.

Updating a Container

Apps in containers get updates just like anything else, to fix bugs and close security holes. Updating a container means fetching a newer image and rebuilding the container from it.

Because your real data lives in the NAS volume folder, not inside the container, rebuilding this way keeps all your settings and files. This is exactly why the volumes chapter mattered so much.

• In the Registry, download the newer version of the app's image.
• Stop the running container.
• Remove the old container - but leave its mapped NAS volume folder alone.
• Create a new container from the newer image, using the same ports and volumes.
• Start it, and check the app works as before.

Stopping and Removing One Cleanly

Trying something and deciding against it is completely normal. Containers are easy to remove cleanly, which is one of the nicest things about them - they do not leave a mess behind.

In Container Manager, select the container, stop it first, then choose to remove it. If you mapped a volume, your data is still in that NAS folder afterward - delete that folder yourself only if you are sure you no longer want the data.

• Stop - pauses the app but keeps the container, ready to start again later.
• Remove - deletes the container entirely. Do this when you are done with it.
• You can also remove the app's downloaded image afterward to free up space.

Setting Resource Limits

A container shares your NAS's power with everything else it does - your files, backups, and photos. You can set gentle limits so one container cannot hog all the memory or processor and slow the rest of the NAS down.

In a container's settings you can cap how much memory it is allowed to use, and how much of the processor it may take. This is a bit like telling a guest they may use the spare room but not the whole house. It keeps one busy app from crowding out your everyday NAS jobs.

• If your NAS has limited memory, set a memory cap so a container cannot use it all.
• Start with modest limits and raise them only if the app clearly needs more.
• Keep an eye on the NAS's resource monitor after adding a container.

Where a Container's Data Actually Lives

It is worth being crystal clear about this, because it is the thing people get wrong most. A container has two very different kinds of storage, and only one of them survives.

So anything the app writes to a mapped NAS volume folder is real, lasting data you can back up and rely on. Anything it keeps only inside the container is temporary and disappears when the container is removed. Whenever data matters, make sure it is going to a volume.

Common Friendly Home Uses

So what do everyday folks actually run in containers? Kept general, here are the kinds of tidy, useful things people set up at home. These stay inside your own network and out of trouble.

The common thread is that these are small, self-contained tools you use inside your own home, from a device on your own Wi-Fi. That is containers at their friendliest - handy, tidy, and low-risk.

• A network ad-blocker - a container that filters out many ads for every device in the house.
• A small personal web app - a simple tool like a notes keeper or a recipe list, just for your household.
• A home dashboard - a single page that shows the status of things around your home.
• A hobby tool - a niche app that has no Synology package, only a container image.

When NOT to Bother

This may be the most useful page in the guide. Containers are powerful, but they are not always the right tool. Often the simpler, safer choice is to skip them entirely.

There is no prize for doing things the hard way. If Package Center has a supported package that meets your need, that is almost always the better choice for a home user. Containers earn their keep only when there is no good package for what you want.

• Synology already offers a proper package that does the same job - use that, it is simpler and supported.
• You only need something basic like file sharing, photos, or backups - DSM's own apps handle these beautifully.
• You are not comfortable reading an app's setup instructions - containers assume you will follow them.
• The only reason to try is curiosity, and the app touches data you cannot afford to lose.

Keeping It Simple

If you do decide to use containers, a handful of calm habits will keep the whole thing pleasant and safe. None of this is hard - it is mostly about going slowly and staying tidy.

Follow those and containers become a quiet, dependable part of your NAS rather than a source of worry. Slow and tidy wins here every single time.

• Add one container at a time, and get it working before adding another.
• Only ever use official or clearly trusted images.
• Map a NAS volume for any data that matters, before you rely on the app.
• Keep containers on your home network - do not expose them to the internet.
• Write down each container's name, ports, and volume folder.
• Include the volume folders in your regular backup.

A Beginner's Container Checklist

Here is the whole journey as one checklist you can run down before, during, and after setting up your first container.

• Confirmed my Synology model actually supports Container Manager.
• Updated DSM and installed Container Manager from Package Center.
• Chose an app I truly need - and checked there is no simpler package for it.
• Downloaded only the official or a clearly trusted image.
• Made a NAS shared folder and mapped it as a volume for the app's data.
• Picked a free port and kept it on my home network only.

What's in the 27-page PDF

• What containers and Docker are, in a plain kitchen analogy
• Whether your Synology model can even run Container Manager
• Installing it and understanding where apps come from
• Ports, volumes, and environment variables without the jargon
• Running, updating, stopping, and removing a container cleanly
• When to bother, when NOT to, and how to stay safe

Why I wrote this

I write these as printable handouts because a guide you can keep in a drawer beats a web page you have to find again. No jargon, no judgment, no rushing. If you'd rather have someone sit beside you and go through it together, that's a flat $99 first visit with the 30-day follow-up included — serving Portage County from Atwater, Ohio. — Bill