Dockerfiles: download opentelemetry-javaagent.jar externally

[paullatzelsperger]

WHAT

Currently the opentelemetry-javaagent.jar is downloaded inside each docker image. For that, we first must install cUrl from Alpine's apk repository. This should be changed so that the opentelemetry-javaagent.jar is downloaded outside the docker image, and copied into the image upon build.

WHY

Code quality analysis tools force us to use explicit versions of cUrl. The version of cUrl changes quite frequently, and Alpine seems to not keep older versions. This means, whenever there is a version upgrade in Alpine, our build pipeline breaks.

Since cUrl is installed manually inside the image with apk, dependabot doesn't pick it up either. This causes random failures in our deployment test pipelines.
Furthermore, downloading the same JAR multiple time is not necessary anyway.

HOW

Create another gradle task that downloads the opentelemetry-javaagent.jar before the docker task, if it's not already present. For example:

val download = { url: String, destFile: File -> ant.invokeMethod("get", mapOf("src" to url, "dest" to destFile)) }

val agentFile = rootDir.resolve("opentelemetry-javaagent.jar")

if (!agentFile.exists()) {
    logger.lifecycle("Downloading OpenTelemetry Agent")
    download("https://github.com/open-telemetry/opentelemetry-java-instrumentation/releases/download/v1.27.0/opentelemetry-javaagent.jar", agentFile)
}