Skeleton for overhead testing subproject. (#3554)

* Skeleton for overhead testing subproject.

* clone into base image instead of submodule

* remove submodules file (even though it was empty)

* use multi-stage dockerfile to simplify image

* strip ssh and add CMD

* use the JRE base for the final stage

testing-overhead/.dockerignore

@@ -0,0 +1,5 @@
+*.hprof
+*.jfr
+*.class
+logs/
+.idea/

testing-overhead/Dockerfile-petclinic-base

@@ -0,0 +1,19 @@
+FROM adoptopenjdk:11-jdk as app-build
+
+# This is the base image that will contain a built version of the spring-petclinic-rest
+# application. Installing the dependencies and maven compiling the application is time
+# consuming, so we do it in a base image to save time nightly.
+
+RUN apt update && apt install -y git
+WORKDIR /app
+RUN git clone http://github.com/spring-petclinic/spring-petclinic-rest.git
+WORKDIR /app/spring-petclinic-rest
+RUN ./mvnw package -Dmaven.test.skip=true
+RUN cp target/spring-petclinic-rest*.jar /app/spring-petclinic-rest.jar
+
+FROM adoptopenjdk:11-jre
+
+COPY --from=app-build /app/spring-petclinic-rest.jar /app/spring-petclinic-rest.jar
+WORKDIR /app
+EXPOSE 9966
+CMD ["java", "-jar", "spring-petclinic-rest.jar"]

testing-overhead/README.md

@@ -0,0 +1,27 @@
+
+# Overhead tests
+
+This is a work in progress. 
+
+This directory will contain tools and utilities
+that help us to measure the performance overhead introduced by 
+the agent and to measure how this overhead changes over time.
+
+## Contents
+
+tbd
+
+## Config
+
+tbd
+
+## Setup and Usage
+
+Once we have an established base image published for `spring-petclinic-rest`, this step
+can be avoided by most users. For now, there is just a spring petclinic base image.
+
+```
+$ docker build -f Dockerfile-petclinic-base .
+```
+
+Remaining usage TBD.