Developer Containers#

Types of Changes#

Containerized IOCs can be modified in 3 distinct places (in order of decreasing frequency of change but increasing complexity):

Changing the IOC instance#

This means making changes to the IOC instance folders which appear in the iocs folder of an ec-services repository. e.g.:

changing the EPICS DB (or the ibek files that generate it)
altering the IOC boot script (or the ibek files that generate it)
changing the version of the Generic IOC used in values.yaml
for Kubernetes: the values.yaml can override any settings used by helm so these can also be adjusted on a per IOC instance basis.
for Kubernetes: changes to the global values.yaml file found in helm/shared, these affect all IOCs in the repository.

Changing the Generic IOC#

This involves altering how the Generic IOC container image is built. This means making changes to an ioc-XXX source repo and publishing a new version of the container image. Types of changes include:

changing the EPICS base version
changing the versions of EPICS support modules compiled into the IOC binary
adding new support modules
altering the system dependencies installed into the container image

Changing the dependencies#

Sometimes you will need to alter the support modules used by the Generic IOC. To make use of these changes would require:

publishing a new release of the support module,
updating and publishing the Generic IOC
updating and publishing the IOC instance

Need for a Developer Container#

For all of the above types of changes, the epics-containers approach allows local testing of the changes before going through the publishing cycle. This allows us to have a fast ‘inner loop’ of development and testing.

Also, epics-containers provides a mechanism for creating a separate workspace for working on all of the above elements in one place.

The earlier tutorials were firmly in the realm of Changing the IOC instance above. It was adequate for us to install a container platform, IDE and python and that is all we needed.

Once you get to level of Changing the Generic IOC you need to have compilers and build tools installed. You might also require system level dependencies. AreaDetector, that we used earlier has a long list of system dependencies that need to be installed in order to compile it. Traditionally we have installed all of these onto developer workstations or separately compiled the dependencies as part of the build.

These tools and dependencies will differ from one Generic IOC to the next.

When using epics-containers we don’t need to install any of these tools or dependencies on our local machine. Instead we can use a developer container, and in fact our Generic IOC is our developer container.

When the CI builds a Generic IOC it creates two targets


developer	this target installs all the build tools and build time dependencies into the container image. It then compiles the support modules and IOC.
runtime	this target installs only the runtime dependencies into the container. It also extracts the built runtime assets from the developer target.

The developer stage of the build is a necessary step in order to get a working runtime container. However, we choose to keep this stage as an additional build target and it then becomes a perfect candidate for a developer container.

VSCode has excellent support for using a container as a development environment. The next section will show you how to use this feature. Note that you can use any IDE that supports remote development in a container, you could also simply launch the developer container in a shell and use it via CLI only.

If you want to use the CLI and terminal based editors like neovim then you should use the developer container CLI to get your developer container started. This means the configuration in .devcontainer/devcontainer.json is used to start the container. This is necessary as that is where the useful host filesystem mounts and other config items are defined. See devcontainer-cli for details.

Starting a Developer Container#

Warning

DLS Users and Redhat Users:

There is a bug in VSCode devcontainers extension at the time of writing that makes it incompatible with podman and an SELinux enabled /tmp directory. This will affect most Redhat users and you will see an error regarding permissions on the /tmp folder when VSCode is building your devcontainer.

Here is a workaround that disables SELinux labels in podman. Paste this into a terminal:

sed -i ~/.config/containers/containers.conf -e '/label=false/d' -e '/^\[containers\]$/a label=false'

Preparation#

For this section we will work with the ADSimDetector Generic IOC that we used in previous tutorials. Let’s go and fetch a version of the Generic IOC source and build it locally.

For the purposes of this tutorial we will place the source in a folder right next to your test beamline bl01t:

# starting from folder bl01t so that the clone is next to bl01t
cd ..
git clone git@github.com:epics-containers/ioc-adsimdetector.git
cd ioc-adsimdetector
./build

This will take a few minutes to complete. A philosophy of epics-containers is that Generic IOCs build all of their own support. This is to avoid problematic dependency trees. For this reason building something as complex as AreaDetector will take a few minutes when you first build it.

A nice thing about containers is that the build is cached so that a second build will be almost instant unless you have changed something that requires some steps to be rebuilt.

Note

Before continuing this tutorial make sure you have not left the IOC bl01t-ea-test-02 running from a previous tutorial. Execute this command outside of the devcontainer to stop it:

ec stop bl01t-ea-test-02

Launching the Developer Container#

In the this section we are going to use vscode to launch a developer container. This means that all vscode terminals and editors will be running inside a container and accessing the container filesystem. This is a very convenient way to work because it makes it possible to archive away the development environment along side the source code. It also means that you can easily share the development environment with other developers.

For epics-containers the generic IOC is the developer container. When you build the developer target of the container in CI it will contain all the build tools and dependencies needed to build the IOC. It will also contain the IOC source code and the support module source code. For this reason we can also use the same developer target image to make the developer container itself. We then have an environment that encompasses all the source you could want to change inside of a Generic IOC, and the tools to build and test it.

It is also important to understand that although your vscode session is entirely inside the container, some of your host folders have been mounted into the container. This is done so that your important changes to source code would not be lost if the container were rebuilt. See Developer Container Layout for details of which host folders are mounted into the container.

Once built, open the project in VSCode:

code .

When it opens, VSCode may prompt you to open in a devcontainer. If not then click the green icon in the bottom left of the VSCode window and select Reopen in Container.

You should now be inside the container. All terminals started in VSCode will be running inside the container. Every file that you open with the VSCode editor will be inside the container.

There are some caveats because some folders are mounted from the host file system. For example, the ioc-adsimdetector project folder is mounted into the container as a volume. It is mounted under /workspaces/ioc-adsimdetector. This means that you can edit the source code from your local machine and the changes will be visible inside the container and outside the container. This is a good thing as you should consider the container filesystem to be a temporary filesystem that will be destroyed when the container is rebuilt or deleted.

Preparing the IOC for Testing#

Note

Troubleshooting: if you are experiencing problems with the devcontainer you can try resetting your vscode and vscode server caches on your host machine. To do this, exit vscode use the following command and restart vscode:

rm -rf ~/.vscode/* ~/.vscode-server/*

Now that you are inside the container you have access to the tools built into it, this includes ibek.

The first commands you should run are as follows:

# open a terminal: Menu -> Terminal -> New Terminal
cd /epics/ioc
make

It is useful to understand that /epics/ioc is a soft link to the IOC source that came with your generic IOC source code. Therefore if you edit this code and recompile it, the changes will be visible inside the container and outside the container. Meaning that the repository ioc-adsimdetector is now showing your changes in it’s ioc folder and you could push them up to GitHub if you wanted.

epics-containers devcontainers have carefully curated host filesystem mounts. This allows the developer environment to look as similar as possible to the runtime container. It also will preserve any important changes that you make in the host file system. This is essential because the container filesystem is temporary and will be destroyed when the container is rebuilt or deleted.

See Developer Container Layout for details of which host folders are mounted into the container.

The IOC source code is entirely boilerplate, /epics/ioc/iocApp/src/Makefile determines which dbd and lib files to link by including two files that ibek generated during the container build. You can see these files in /epics/support/configure/lib_list and /epics/support/configure/dbd_list.

Although all Generic IOCs derived from ioc-template start out with the same generic source, you are free to change them if there is a need for different compilation options etc.

The Generic IOC should now be ready to run inside of the container. To do this:

cd /epics/ioc
./start.sh

You will just see the default output of a Generic IOC that has no Instance configuration. Hit Ctrl-C to stop the this default script.

Next we will add some instance configuration from one of the IOC instances in the bl01t beamline.

To do this we will add some other folders to our VSCode workspace to make it easier to work with bl01t and to investigate the container filesystem.

Adding the Beamline to the Workspace#

To meaningfully test the Generic IOC we will need an instance to test it against. We will use the bl01t beamline that you already made. The devcontainer has been configured to mount some useful host folders into the container including the parent folder of the workspace as /workspaces so we can work on multiple peer projects.

In VSCode click the File menu and select Add Folder to Workspace. Navigate to /workspaces and you will see all the peers of your ioc-adsimdetector folder (see Developer Container Layout below). Choose the bl01t folder and add it to the workspace - you may see an error but if so clicking “Cancel” will clear it.

Also take this opportunity to add the folder /epics to the workspace. This is the root folder in which all of the EPICS source and built files are located.

Note

Docker Users: your account inside the container will not be the owner of /epics files. vscode may try to open the repos in epics-base and support/* and git will complain about ownership. You can cancel out of these errors as you should not edit project folders inside of /epics - they were built by the container and should be considered immutable. We will learn how to work on support modules in later tutorials. This error should only be seen on first launch. podman users will have no such problem because they will be root inside the container and root built the container.

To mitigate this problem you can tell vscode not to look for git repos in subfolders, see Disable recursive search for git repositories.

You can now easily browse around the /epics folder and see all the support modules and epics-base. This will give you a feel for the layout of files in the container. Here is a summary (where WS is your workspace on your host. i.e. the root folder under which your projects are all cloned):

Developer Container Layout#
Path Inside Container	Host Mount Path	Description
/epics/support	N/A	root of compiled support modules
/epics/epics-base	N/A	compiled epics-base
/epics/ioc	WS/ioc-adsimdetector/ioc	soft link to IOC source tree
/epics/runtime	N/A	generated startup script and EPICS database files
/epics/ibek-defs	N/A	All ibek Support yaml files
/epics/pvi-defs	N/A	all PVI definitions from support modules
/epics/opi	N/A	all OPI files (generated or copied from support)
/workspaces	WS	all peers to Generic IOC source repo
/workspaces/ioc-adsimdetector	WS/ioc-adsimdetector	Generic IOC source repo (in this example)
/epics/generic-source	WS/ioc-adsimdetector	A second - fixed location mount of the Generic IOC source repo to allow ibek to find it easily.

IMPORTANT: remember that the container filesystem is temporary and will be destroyed when the container is rebuilt or deleted. All folders above with Host Mount Path N/A are in the container filesystem. The devcontainer has been configured to mount the most useful host folders, but note that all support modules are in the container filesystem. Later we will learn how to work on support modules, first ensuring that they are made available in the host filesystem.

Also note that VSCode keeps your developer container until you rebuild it or explicitly delete it. Restarting your PC and coming back to the same devcontainer does keep all state. This can make you complacent about doing work in the container filesystem, but it is still not recommended.

Choose the IOC Instance to Test#

Now that we have the beamline repo visible in our container we can easily supply some instance configuration to the Generic IOC. This will use the ibek tool convenience function dev instance which declares which IOC instance you want to work on in the developer container.

Try the following:

cd /epics/ioc
ibek dev instance /workspaces/bl01t/services/bl01t-ea-test-02
# check the it worked - should see a symlink to the config folder
ls -l config
./start.sh

This removed any existing config folder and replaced it with the config from the IOC instance bl01t-ea-test-02 by symlinking to that IOC Instance’s config folder. Note that we used a soft link, this means we can edit the config, restart the IOC to test it and the changes will already be in place in the beamline repository. You could therefore open a shell onto the beamline repository at /workspaces/bl01t and commit and push the changes.

Wrapping Up#

We now have a tidy development environment for working on the Generic IOC, IOC Instances and even the support modules inside the Generic IOC, all in one place. We can easily test our changes in place too. In particular note that we are able to test changes without having to go through a container build cycle.

In the following tutorials we will look at how to make changes at each of the 3 levels listed in Types of Changes.