Add ubi-min based images

[leochr]

Add ubi-min based images for kernel-slim and full. Use the Semeru JRE image (as opposed to JDK) as the base.

[leochr]

Some investigation is needed to evaluate whether UBI-min based images would significantly reduce the size of Liberty images. Build ubi-min based image for kernel-slim tag (with OpenJ9 Java 8) and compare to relevant ubi based image

[dougbreaux]

I came looking for this because cloud security best practices say to use the smallest image you can. And the Ubuntu images are smaller than the UBI ones.

[jdmcclur]

Another option is basing our images on ubi-jre instead of ubi.
Example: adoptopenjdk/openjdk8-openj9:ubi-jre vs adoptopenjdk/openjdk8-openj9:ubi

I think ubi-jre only packages the jre instead of the whole jdk.

For our ubuntu images we use jre images, so I would think we would want to do the same for ubi?

adoptopenjdk/openjdk11-openj9       ubi          590MB
adoptopenjdk/openjdk11-openj9       ubi-jre      376MB
adoptopenjdk/openjdk8-openj9        ubi          479MB
adoptopenjdk/openjdk8-openj9        ubi-jre      378MB

[arthurdm]

There is also now ubi-micro. I've asked here for plans to support it.

[matthewpwilson]

@verymahler please can you tell me which images are based on ubi-mimimal?

[verymahler]

@matthewpwilson They aren't. I removed my comment.

[lmsurpre]

@leochr is there any update on this? your comment on the PR says:

Once the images are in icr.io, the Liberty images will need to switch to those.

But its been over 6 months...is the Semeru runtimes team planning to make ubi-min (or ubi-micro) images available?