Adds health-check functionality to local image

Adds health-check script to template.

Alters Dockerfile to import health-check script and adds `HEALTHCHECK`
directive.

All container documentation is in master branch.

Author: Paraphraser

.internal/templates/services/mosquitto/buildFiles/Dockerfile

@@ -13,6 +13,18 @@ ENV IOTSTACK_DEFAULTS_DIR="iotstack_defaults"
 # copy template files to image
 COPY --chown=mosquitto:mosquitto ${IOTSTACK_DEFAULTS_DIR} /${IOTSTACK_DEFAULTS_DIR}
 
+# copy the health-check script into place
+ENV HEALTHCHECK_SCRIPT "iotstack_healthcheck.sh"
+COPY ${HEALTHCHECK_SCRIPT} /usr/local/bin/${HEALTHCHECK_SCRIPT}
+
+# define the health check
+HEALTHCHECK \
+   --start-period=30s \
+   --interval=30s \
+   --timeout=10s \
+   --retries=3 \
+   CMD ${HEALTHCHECK_SCRIPT} || exit 1
+
 # replace the docker entry-point script
 ENV IOTSTACK_ENTRY_POINT="docker-entrypoint.sh"
 COPY ${IOTSTACK_ENTRY_POINT} /${IOTSTACK_ENTRY_POINT}

.internal/templates/services/mosquitto/buildFiles/iotstack_healthcheck.sh

@@ -0,0 +1,64 @@
+#!/usr/bin/env sh
+
+# assume the following environment variables, all of which may be null
+#    HEALTHCHECK_PORT
+#    HEALTHCHECK_USER
+#    HEALTHCHECK_PASSWORD
+#    HEALTHCHECK_TOPIC
+
+# set a default for the port
+HEALTHCHECK_PORT="${HEALTHCHECK_PORT:-1883}"
+
+# strip any quotes from username and password
+HEALTHCHECK_USER="$(eval echo $HEALTHCHECK_USER)"
+HEALTHCHECK_PASSWORD="$(eval echo $HEALTHCHECK_PASSWORD)"
+
+# set a default for the topic
+HEALTHCHECK_TOPIC="${HEALTHCHECK_TOPIC:-iotstack/mosquitto/healthcheck}"
+HEALTHCHECK_TOPIC="$(eval echo $HEALTHCHECK_TOPIC)"
+
+# record the current date and time for the test payload
+PUBLISH=$(date)
+
+# publish a retained message containing the timestamp
+mosquitto_pub \
+   -h localhost \
+   -p "$HEALTHCHECK_PORT" \
+   -t "$HEALTHCHECK_TOPIC" \
+   -m "$PUBLISH" \
+   -u "$HEALTHCHECK_USER" \
+   -P "$HEALTHCHECK_PASSWORD" \
+   -r
+
+# did that succeed?
+if [ $? -eq 0 ] ; then
+
+   # yes! now, subscribe to that same topic with a 2-second timeout
+   # plus returning on the first message
+   SUBSCRIBE=$(mosquitto_sub \
+                -h localhost \
+                -p "$HEALTHCHECK_PORT" \
+                -t "$HEALTHCHECK_TOPIC" \
+                -u "$HEALTHCHECK_USER" \
+                -P "$HEALTHCHECK_PASSWORD" \
+                -W 2 \
+                -C 1 \
+              )
+
+   # did the subscribe succeed?
+   if [ $? -eq 0 ] ; then
+
+      # yes! do the publish and subscribe payloads compare equal?
+      if [ "$PUBLISH" = "$SUBSCRIBE" ] ; then
+
+         # yes! return success
+         exit 0
+
+      fi
+
+   fi
+   
+fi
+
+# otherwise, return failure
+exit 1