Dev Container vs Runtime Container#

Introduction#

The dev container is where all development of IOCs and support modules will take place. The runtime container is where the IOC will run when deployed to a target system.

The dev container mounts several host folders into the container to achieve the following goals:

make the developer container look as similar as possible to the runtime container
allow the developer to make changes and recompile things without having to rebuild the container
make sure that all useful changes occur in the host filesystem so that they are not lost when the container is rebuilt or deleted

The details of which folders are mounted where in the container are shown here: Generic IOC Container Filesystem Layout.

The ioc-XXX project folder is found in the container at /workspaces/ioc-XXX, along with all of it’s peers (because the parent folder is mounted at /workspaces).

The ioc Folder#

The ioc folder contains the Generic IOC source code. It is typically the same for all Generic IOCs but is included in the ioc-XXX repo in /ioc so that it can be modified if necessary.

At container build time this folder is copied into the container at /epics/generic-source/ioc and it is compiled so that the binaries are available at runtime.

In the dev container the /epics/generic-source folder has the project folder ioc-XXX mounted over the top of it. This means:

the project folder ioc-XXX is mounted in two locations in the container - /workspaces/ioc-XXX - /epics/generic-source
the ioc source folder /epics/generic-source/ioc is also mounted over and now contains the source only. The compiled binaries are no longer visible inside the dev container.

It is for this reason that a newly created dev container needs to have the IOC binaries re-compiled. But this is a good thing, because now any changes you make to the IOC source code can be compiled and tested, but also those changes are now visible on the host filesystem inside the project folder ioc-XXX/ioc. This avoids loss of work.

Finally the ioc folder is always soft linked from /epics/ioc so that the source and binaries are always in a known location.

Summing Up#

The above description makes things sound rather complicated. However, you can for the most part ignore the details and just remember:

use /epics/ioc to compile and run the IOC.
you are free to make changes to the above folder and recompile
the changes you make will be visible on the host filesystem in the original project folder.