explain how to debug a build

Debug-In-OpenShift/README.md

@@ -65,4 +65,51 @@ ps ax
 **and then:**
 ```sh
 strace -ff -p <pid>
-```
+```
+
+## Debug a Build Job
+
+Let's say that a Java build is failing and you need to troubleshoot the issue.
+For the record, let's pretend it's a Java build based on maven. For instance,
+you are trying to build [openshift-tasks](https://github.com/lbroudoux/openshift-tasks/tree/eap-7)
+application.
+
+Spawn a persistent Build Pod and get a shell on this pod:
+
+```sh
+oc new-app --name java-debug redhat-openjdk18-openshift:1.2
+oc patch dc java-debug --type=json -p '[{"op": "add", "path": "/spec/template/spec/containers/0/command", "value": ["/bin/sh", "-c", "while :; do sleep 1; done" ]}]'
+oc get pods
+oc rsh $(oc get pods -l app=java-debug -o name|tail -n 1)
+```
+
+Since the Maven has been installed in the container using the Software
+Collections, you will need to enable this environment with:
+
+```sh
+scl -l
+scl enable rh-maven33 /bin/bash
+```
+
+The source code is usually fetched using GIT but from another container.
+So, to fetch the source code to build, you can do a `git clone` and pack it from
+another machine or if you are using GitHub, you can directly fetch a ZIP:
+
+```sh
+curl -Lo /tmp/src.zip https://github.com/lbroudoux/openshift-tasks/zipball/eap-7
+```
+
+Unpack it:
+
+```sh
+mkdir -p /tmp/src
+cd /tmp/src
+unzip /tmp/src.zip
+```
+
+And then, replicate what the S2I build is doing:
+
+```sh
+cd lbroudoux-openshift-tasks-d745675
+/usr/local/s2i/assemble
+```