mq-container/docs/internals.md

Internals

This page documents internal code details and design decisions.

The resulting Docker image contains the following:

• Base linux distribution - this provides standard Linux libraries (such as "glibc") and utilities (such as "ls" and "grep") required by MQ
• MQ installation (under /opt/mqm)
• Three additional programs, to enable running in a containerized environment:
  • runmqserver - The main process, which creates and runs a queue manager
  • runmqdevserver - The main process for MQ Advanced for Developers
  • chkmqhealthy - Checks the health of the queue manager. This can be used by (say) a Kubernetes liveness probe.
  • chkmqready - Checks if the queue manager is ready for work. This can be used by (say) a Kubernetes readiness probe.

runmqserver

The runmqserver command has the following responsibilities:

• Checks license acceptance
• Sets up /var/mqm
  • MQ data directory needs to be set up at container creation time. This is done using the crtmqdir utility, which was introduced in MQ V9.0.3
  • It assumes that a storage volume for data is mounted under /mnt/mqm. It creates a sub-directory for the MQ data, so /var/mqm is a symlink which resolves to /mnt/mqm/data. The reason for this is that it's not always possible to change the ownership of an NFS mount point directly (/var/mqm needs to be owned by "mqm"), but you can change the ownership of a sub-directory.
• Acts like a daemon
  • Handles UNIX signals, like SIGTERM
  • Works as PID 1, so is responsible for reaping zombie processes
• Creating and starting a queue manager
• Configuring the queue manager, by running any MQSC scripts found under /etc/mqm
• Indicates to the chkmqready command that configuration is complete, and that normal readiness checking can happen. This is done by writing a file into /run/runmqserver

In addition, for MQ Advanced for Developers only, the web server is started.

runmqdevserver

The runmqdevserver command is added to the MQ Advanced for Developers image only. It does the following, before invoking runmqserver:

1. Sets passwords based on supplied environment variables
2. Generates MQSC files to put in /etc/mqm, based on a template, which is updated with values based on supplied environment variables.
3. If requested, it creates TLS key stores under /run/runmqdevserver, and configures MQ and the web server to use them

A special version of runmqserver is used in the developer image, which performs extra actions like starting the web server. This is built using the mqdev build constraint.