Openshift v3 (3.2)

Read it first

• Best Practices building Docker containers
• Best Practices building Docker images for Openshift

Docker Containers: if you want to change your distribution base to RHEL/CentOS

When we have dockerfiles that are not RHEL/CentOS based, if we want to migrate.

Change your base image

Example

substitute FROM debian:wheezy to FROM centos:centos7

Change the package manager

Move to "yum" if possible. If not, "rpm" should be used. If the original distribution used apt, it should be analyse the package translation:

RUN apt-get update && \
	apt-get install -y "gcc" --no-install-recommends \ 
	gcc … && \
	apt-get purge -y --auto-remove "gcc"

We find out that gcc is needed to build the image, so it is installed with apt-get and then removed. Equivalent with CentOS: first we identify which package includes gcc. We execute:

yum whatprovides gcc

Loaded plugins: fastestmirror, langpacks
Determining fastest mirrors
 * base: centos.cadt.com
 * extras: centos.cadt.com
 * updates: centos.cadt.com
gcc-4.8.3-9.el7.x86_64 : Various compilers (C, C++, Objective-C, Java, ...)
Repo        : base

From that package, we can use short-name (without version), if there is no both 32 (i686) and 64 bits (x86_64). The above command in CentOS will be:

RUN yum -y --setopt=tsflags=nodocs install gcc && \
	gcc "…" && \
	yum -y remove gcc \
	yum -y clean all 

RHEL 7

If we want to use RHEL instead, we need to know which repository should be enabled before running "yum":

yum whatprovides gcc

Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-manager
gcc-4.8.2-16.el7.x86_64 : Various compilers (C, C++, Objective-C, Java, ...)
Repo        : rhel-7-server-rpms

Then, the dockerfile should include previously:

RUN yum install -y yum-utils gettext hostname && \
        yum-config-manager --enable rhel-7-server-rpms && \
        yum -y --setopt=tsflags=nodocs install gcc…

Which has to be executed from RHEL with docker, otherwise you will not have authorization to enable those repos in the build!

Applications executed with root or with a named-user

If those applications has some priviledges requirements on some fields/ports, some further changes should be implemented. Those changes will include:

• Grants to files/folders
• Port changes from protected (=<1024) to non-protected (>1024)

Openshift Templates

First steps

First, Openshift Templates should be read

Tips & Tricks

• For rapid prototyping, try to use docker hub "official" images if possible.
• Some development templates needs persistent volumes. First, start with ephemeral ones, then add the volumes at a later stage.
• If you need to change the configuration, there are different alternatives.
  • Kubernetes ConfigMaps if you need some config files in a single folder
  • Github volume mount for a whole set of files in a definite structure (for example, plugin jars)
  • Persistent volumes for dev iteration

Testing

A first test (grammar) can be done with "oc" client.

$ oc process -o describe -f template.json 

A next test should be instantiating our template, checking that every object is created. Additionally, we need to check:

• Volume mounts are ok
• Pods are starting and running correctly