README for jlink template directory

Signed-off-by: Jonathan Dowland <[email protected]>

Author: jmtd

templates/jlink/Dockerfile

@@ -3,7 +3,7 @@
 #Stage-1:build application JAR and libraries
 #steps to build the application JAR and jlinked JRE
 #for time being using the image built by Jon
-FROM quay.io/jdowland/jlink:quarkus-getting-started AS ubi9-jlinked-image
+FROM ubi9-jlinked-image AS ubi9-jlinked-image
 USER 0
 RUN mkdir -p /mnt/jrootfs
 RUN microdnf install dnf -y

templates/jlink/README.md

@@ -0,0 +1,56 @@
+# OpenShift-JLink PoC
+
+Try it out:
+
+## Stage 1: build and analyse application with OpenShift source-to-image (S2I)
+
+You need:
+
+1. Access to an OpenShift instance, or, use [the s2i standalone program](https://github.com/openshift/source-to-image)
+    * _([you might need to use an old version](https://github.com/openshift/source-to-image/issues/1135))_
+2. The OpenJDK builder image (with the customisations from the `jlink-dev` branch).
+   There's one at `quay.io/jdowland/jlink:latest`
+3. A quickstart ([there's a specially-prepared Quarkus quickstart](https://github.com/jmtd/quarkus-quickstarts/tree/OPENJDK-631-fastjar-layout);
+   in the future [the mainline Quarkus quickstarts will be suitable](https://github.com/quarkusio/quarkus-quickstarts/pull/1359))
+
+Here's a recipe using local `s2i`
+
+```
+BASEIMG=quay.io/jdowland/jlink:latest
+APPSRC=https://github.com/jmtd/quarkus-quickstarts.git
+CONTEXTDIR=getting-started
+REV=OPENJDK-631-fastjar-layout
+OUTIMG=ubi9-jlinked-image
+
+s2i build --pull-policy never --context-dir=${CONTEXTDIR} -r=${REV} \
+    -e QUARKUS_PACKAGE_TYPE=uber-jar \
+    -e S2I_ENABLE_JLINK=true \
+    ${APPSRC} \
+    ${BASEIMG} \
+    ${OUTIMG}
+```
+
+## Stage 2: multi-stage build to assemble micro runtime
+
+You need:
+
+1. The output image from the first stage
+    * _here's one we made earlier: `quay.io/jdowland/jlink:quarkus-getting-started`_
+2. OpenShift, or a container runtime (e.g. Docker)
+3. [this Dockerfile](Dockerfile) (In future this is an OpenShift template)
+
+With docker, from a clone of this repository, in this directory:
+
+```
+docker build -t myapp -f .
+```
+
+## Stage 3: try it out!
+
+Does it work?
+
+    docker run --rm -ti -p 8080 myapp
+
+How big is it?
+
+    docker inspect -f '{{.Size}}' myapp