Update run-in-container.sh script

Add detailed information on how to perform the task manually.

scripts/run-in-container.sh

@@ -1,23 +1,66 @@
 #!/bin/bash
 
-# Use this script to run one-off commands inside a container of a pod
-# (where your application code lives in)
+# Use this script to run one-off commands inside a container of a pod where your
+# Python application code lives in.
+
+# You can accomplish the same results by using regular commands from OpenShift.
+# This script is just wrapping calls to `osc` to make it a little more
+# convenient to use. In the future, the `osc` cli tool might incorporate changes
+# that make this script obsolete.
+
+# Here is how you would run a command in a pod specified by label [1]:
 #
-# Examples:
-# ./run-in-container.sh web date
-# ./run-in-container.sh database env
-# ./run-in-container.sh web ./manage.py migrate
-# ./run-in-container.sh web ./manage.py createsuperuser
-# ./run-in-container.sh web tail -f access.log
-# POD_INDEX=1 ./run-in-container.sh web tail -f access.log
+# 1. Inpect the output of the command below to find the name of a pod that
+#    matches a given label:
+#
+#     osc get pods -l <your-label-selector>
+#
+# 2. Open a bash shell in the pod of your choice:
+#
+#     osc exec -p <pod-name> -it -- bash
+#
+# 3. Because of how `kubectl exec` and `osc exec` work right now [2], your
+#    current working directory is root (/). Change it to where your code lives:
+#
+#     cd $HOME
+#
+# 4. Because of how the images produced with CentOS and RHEL work currently [3],
+#    you need to manually enable any Software Collections you need to use:
+#
+#     source scl_source enable python33
+#
+# 5. Finally, execute any command that you need and exit the shell.
+#
+# Related GitHub issues:
+# [1] https://github.com/GoogleCloudPlatform/kubernetes/issues/8876
+# [2] https://github.com/GoogleCloudPlatform/kubernetes/issues/7770
+# [3] https://github.com/openshift/origin/issues/2001
 
-POD_NAME="$1"
-if [[ -z "$POD_NAME" ]]; then
-  echo "missing pod name"
-  exit 1
-fi
-shift
 
-quoted_args="$(printf " %q" "${@:-echo}")"
-osc exec -p $(osc get pods -l "name=$POD_NAME" -t "{{ with index .items ${POD_INDEX:-0} }}{{ .metadata.name }}{{ end }}") -it -- bash -c "cd \$HOME && scl enable python33 \"$quoted_args\""
+# You can use this wrapper like this:
+#
+#     ./run-in-container.sh ./manage.py migrate
+#     ./run-in-container.sh ./manage.py createsuperuser
+#     ./run-in-container.sh tail -f access.log
+#
+# If your Python pods are labeled with a name other than "web", you can use:
+#
+#     POD_NAME=something ./run-in-container.sh ./manage.py check
+#
+# You can also specify a POD by index:
+#
+#     POD_INDEX=1 ./run-in-container.sh tail -f access.log
+#
+# Or both together:
+#
+#     POD_NAME=frontend POD_INDEX=2 ./run-in-container.sh tail -f access.log
 
+
+# Get name of a currently deployed pod by label and index
+POD_INSTANCE_NAME=`osc get pods \
+  -l "name=${POD_NAME:-web}" \
+  -t "{{ with index .items ${POD_INDEX:-0} }}{{ .metadata.name }}{{ end }}"`
+
+# Run command in a container of the specified pod:
+osc exec -p "$POD_INSTANCE_NAME" -it -- bash -c \
+  "cd \$HOME && source scl_source enable python33 && ${@:-echo}"