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Re: few basic questions about S2I and docker run

On Fri, Aug 26, 2016 at 1:07 PM, Ravi <ravikapoor101 gmail com> wrote:

So I am trying to use openshift to manage our dockers.

First problem I am facing is that most of documentation and image templates seem to be about S2I. We are

​When it comes to building images, openshift supports basically 4 approaches, in descending order of recommendation and increasing order of flexibility:

1) s2i (you supply source and pick a builder image, we build a new application image and push it somewhere)
2) docker-type builds (you supply the dockerfile and content, we run docker build for you and push the image somewhere)
3) custom​ (you supply an image, we'll run that image, it can do whatever it wants to "build" something and push it somewhere, whether that something is an image, jar file, etc)
4) build your images externally on your own infrastructure and just use openshift to run them.

The first (3) of those are discussed here:
considering a continuous builds for multiple projects and building an image every 1 hour for multiple projects would create total 20GB images every day.

I'm not sure how this statement relates to s2i.  Do yo have a specific concern about s2i with respect to creating these images?  Openshift does offer image pruning to help deal with the number of images you sound like you'll be creating, if you're interested in that.


Q1: Is this right way of thinking? Since today most companies are doing CI, this should be a common problem. Why is S2I considered impressive feature?

​S2I really has little to do with CI/CD.  S2I is one way to produce docker images, there are others as I listed above.  Your CI flow is going to be something like:

1) change source
2) build that source into an image (in whatever way you want, s2i is one mechanism)
3) test the new image
4) push the new image into production

​The advantages to using s2i are not about how it specifically works well with CI, but rather with the advantages it offers around building images in a quick, secure, convenient way, as described here:


So, I am trying to use off the shelf images and inject code/conf into them. I know how to do this from docker command line (example: docker run --rm -it -v /my/host/folder:/usr/src/myapp -w /usr/src/myapp openjdk:8-jre-alpine java myClass )

​That is not a great approach to running code.  It's fine for development, but you really want to be producing immutable images that a developer can hand to QE has tested it, they can hand that exact same image to prod, and there's no risk that pieces have changed.

Also running things in that way means you need to get both the image and your class files into paths on any machine where the image is going to be run, and then specify that mount path correctly.  It's not a scalable model.  You want to build runnable images, not images that need the application side-loaded via a mount.


Q2: How do I configure exact same command from openshift? I will need to do following steps

You shouldn't.  Strictly speaking you can, via pod mount definitions and hostpath volume definitions, but it's not the right way to think about creating and running images in a clustered environment.​

1. Jenkins is pushing compiled jar files to git repository. First step will be to pull the files down.
2. I may have to unzip some files (in case it is bunch of configurations etc.)
3. Openshift should use docker run to create containers.

​Assuming you want to continue building jars via jenkins and pushing them somewhere (doesn't have to be git), i'd suggest the following flow:

1) jenkins builds jar and pushes it somewhere
2) an s2i(or docker) build in openshift pulls from that somewhere (either it's pulling the git source that includes the jar, or you can write your own assemble script which pulls the jar from a nexus repo(or a dockerfile which does so) or some other location.  This is discussed here:   https://docs.openshift.org/latest/dev_guide/builds.html#using-external-artifacts)

You can also do binary builds which don't require you put the content in a git repo:

in which case the jenkins job would build the jar locally and then invoke "oc start-build yourbuild --from-file your.jar"

​3) the image will get pushed to a docker registry as part of the build
4) the image gets deployed on openshift, it is fully self-contained and does not need any external mounts.  It can scale up and move between host nodes without any adminstrative maintenance.

Hope that helps.


thanks so much for help

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