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This is a companion page to a Yale git repository with the files to do the build.

This is a generic project to create Docker images to run Yale applications. It should be possible to build an image on the developer’s machine for testing, then check the project into git.yale.edu and run the Jenkins job to built the image for the Yale container runtime environment.

Requirements

  • The Jenkins job builds an image using just the Dockerfile with no custom parameters. Therefore, the Dockerfile all by itself must build and image for the Yale environment, while files in this project override build args and provide additional tags only on the developer’s desktop.

  • The exact method of doing the equivalent of a “docker build” on the desktop is defined by the developer in a profile. It is possible to use a local docker command, or a remote ssh docker command, or a substitute for Docker like Podman.

  • Each user provides a profile that defines the Sandbox environment (the local substitute for Artifactory and Harbor for example) and the personal choices (the use of a local docker, remote docker, or substitute).

  • A script file is included in every project to define any project specific overrides. For example, the Dockerfile may contain a reference to a Released artifact version such as 1.0.19 while the script may contain the developer’s override version 1.0.20-SANDBOX.

General Approach

Whenever there is a value in the Dockerfile that should be different in the Sandbox from the Jenkins build value, create an ARG and set the default to match the value in Jenkins. Then you can override this ARG value by adding a --build-arg parameter to the “docker build”.

Examples:
ARG ARTIFACT_SERVER=https://repository.its.yale.edu/artifactory/libs-releases-local
ARG YaleArtifactVersion=1.0.48

he ARG ARTIFACT_SERVER would typically not be in the build.json file because it is a permanent part of the developer desktop configuration. If the user provides a local artifact server URL, it will be set in the user’s $HOME\sandboxProfile.ps1 file:
$SANDBOX_ARTIFACT_SERVER="http://repository.yale.sandbox/artifactory"

Putting the project specific --build-arg overrides in the script means that every script file is unnecessarily unique. Instead, the override values are stored in a build.json file in the project which is read by code in the profile script and automatically generates the override parameters.

{
    "new_image_tag": "iiq:8.1p1-yale-1.0.48",
    "build_arg": {
      "YaleArtifactVersion": "1.0.48-SNAPSHOT",
      "SailpointVersion": "8.1p1"
    }
}

The only parameter required in the build.json file is the “new_image_tag” which is unique for each project and cannot be specified in the Dockerfile (but must be a -t on the “docker build” command).

The project specific build.ps1 script defines variables, includes the Profile script, and then calls the build-image command generated by the profile script. Most build.ps1 files are minimal and identical with this common content.

if (test-path $HOME\SandboxProfile.ps1) {
    . $HOME\SandboxProfile.ps1 
    build-image
} else {
    Write-Host "You have no $HOME/SandboxProfile.ps1 file. Get if from https://git.yale.edu/gilbert/SandboxImageBuild"
}

Remember, the build.ps1 and build.json files are checked into the Git project but are not used by the Jenkins build. While they contain information for you, they are mostly intended to help the next developers who works on this project, providing an example of things that they may want to customize.

Parameters for the Build

Most parameters like --build-arg and -t are described in the Docker documentation and have obvious uses. Two parameters are always supplied by Jenkins and turn out to be very useful for developers as well. They are more obscure and should be explained:

--no-cache disables a Docker optimization which caches the results of each line in the Dockerfile and in a subsequent run of the same file, uses the results from the previous run instead of re-executing the statement. This might be occasionally helpful if you have a very long running statement that never changes, but in practice it is often a bad optimization. There are some statements that reference things in the network that change over time, and though the statement itself has not changed, the results are different. An example everyone may use is

“RUN apt update && apt upgrade -Y”

You expect this to put all the currently available fixes on the image, but if this was run and cached a month ago then Docker will reuse the result, which omits fixes added in the last month. There are less obvious examples that suggest that --no-cache is a better default.

--pull is a special version of --no-cache that applies to the image in the FROM statement. A DockerHub image like “tomcat:latest” is periodically updated with the latest version and fixes. Nobody would use it, but more specific tags that require jdk11 and tomcat 9 will still be automatically update with the latest version of 9 and the latest fixes to jdk11. When you use a base image name that is periodically updated, and you want to get the most recent version, you have to specific --pull on the docker build or docker will use the previous image that it pulled which had the same tag name.

Base Image Choice

If you look at all the Tomcat tags in DockerHub, you will find versions based on several distributions. Currently Debian is the simplest distribution that remains current and has fixes for all reported vulnerabilities.

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