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Howard Gilbert

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  • 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 and is run only on the developer desktop to do that type of build. The project specific script file includes project specific parameters while the generic code shared by all projects built by this developer are in the developer’s profile script.

  • The developer may run a copy of Harbor on his machine, or may choose to scan images and share images across VMs using a different method. All images are tagged on the developer machine with the same prefixes they will have in the Yale Harbor server.

General Approach

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  • 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.

ARGs

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

Overrides for ARG values and other properties 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 that is only used on the developer desktopwhich is read by code in the profile script and automatically generates the override parameters.

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

The smallest only parameter required in the build.json file contains only is the “new_image_tag” because the tag is generated from the Jenkins job parameters and is not in the Dockerfile, so this is the only place it can come from on the developer’s desktop.

Note that the ARG YaleArtifactVersion default is a “production” version number (after a Perform Release has been done), while the override value in the JSON is the -SNAPSHOT version number used while developing before you generate a Release.

A best practice is that when an image contains a Yale Artifact, the Artifact Version number is in the image tag, so it is easy to tell what version of the application was put into the image.

The 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"

The the profile will add it to the list of --build-arg parameters passed to the “docker build” command:

Code Block
$build_args=[System.Collections.ArrayList]@( `
    "--build-arg ARTIFACT_SERVER=$SANDBOX_ARTIFACT_SERVER", `
    "--build-arg IMAGE_REGISTRY=$SANDBOX_IMAGE_REGISTRY" `
    )

The convention is for the profile to expose a build-image command and to have the individual build.ps1 file in each project call that function to do the “docker build” or its equivalent. There are alternate approaches to do a “wsl docker build” (run it in WSL), or “ssh userid@vm docker build” (run it on a VM), or “multipass exec vm docker build” (special version of ssh for Multipass), or “wsl podman build” (run podman replacement for docker in WSL), or “nerdctl build” (Rancher desktop). By putting the actual command in the profile script, the user can choose which technology he prefers to use.

Parameters for the Build

There are a few parameters that the Jenkins job always puts on the “docker build”, and they are probably a good choice for you to add to your environment

--no-cache causes the build to execute each step in the Dockerfile even if that line has not changed and there is a cached result from the previous execution of that line. Generally our Dockerfiles are not that big and complicated, and allowing Docker to reuse the cached results of executing a previous Dockerfile produces unfortunate results. For example, a 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.

Code Block
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.

Remove Bad Optimization

Docker has two default behaviors that over optimize the build process and generate mistakes. These should be suppressed by adding parameters to turn them off.

--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 (or any file that starts out the same), uses the saved results from the previous run instead of re-executing the statement. While this may save a few seconds, it produces unexpected behavior and is counter intuitive. The problem occurs with statements that get files or packages from the network. The Dockerfile statement is expected to get the most current files and not some files downloaded and saved months ago. This can happen with all sorts of statements, but the one example that makes the problem clear is the commonly used expression to apply the most recent bugfixes to the system:

“RUN apt update && apt upgrade -Y” is probably intended to install all the very latest fixes and not the fixes that were cached from running these commands a few months ago. Dockerfile line caching produces unexpected results and should not be the default for unsuspecting users

Since this statement itself doesn’t change, the default behavior of Docker is to download fixes the first time you build the image, and then never apply any new patches to any future build. Specifying --no-cache runs the entire Dockerfile fresh every time.

--pull is a special version of --no-cache that applies to the image in the FROM statement. By default, Docker doesn’t check to see if there is a new version of the image in the source repository (DockerHub?) when you already have an image downloaded with the same tag. This is OK if the tag is specific to a particular unchanging version. However, when you are referencing a “latest” image, then you may want to replace an old base image with an updated version with bugs fixed and you need to suppress the unwelcome Docker optimization by forcing it to --pull a newer image if one is available.

Base Image Choice

The most common choice for Docker Hub images is Debian. When it became common to scan images for vulnerabilities, Debian was initially slow to respond. Today, however, they have a special package source URL for vulnerability fixes and make a fix available as soon as the vulnerability is announced. This is, therefore, the best choice when looking for a clean scanA DockerHub image like “tomcat:latest” is periodically updated with the latest version and fixes. A more reasonable choice for a base image specifies a particular version of Java and Tomcat, but then allows the latest dot release with bug fixes. The default Docker behavior is to download a base image and then never check DockerHub for a newer version of the image as long as the tag doesn’t change. Adding --pull causes Docker to check for a more recent version of the base image and pull one if it is available.

Base Choice

The official Tomcat images offer versions of OpenJDK from various sources (Amazon, Eclipse, etc.) and various releases of Debian and Ubuntu.

Plain OpenJDK and the most recent release of Debian seem to be good choices, and Debian has a special package repository that is quickly updated whenever a vulnerability is announced.