Adding Kong integration guide

Signed-off-by: Jono Finger <jono@foodnotblogs.com>

guide/kong_integration.md

+# Using Kong as an API gateway for OpenFaaS
+
+[Kong](https://getkong.org) is an API gateway that provides features such as security, logging, and rate limiting. By putting this in front of OpenFaaS you can quickly get access to these things and a lot more via [the many other plugins written](https://getkong.org/plugins/) for it.
+
+Below is a demo of how you could use Kong as an authentication layer for OpenFaaS. You should be able to paste this all (from its Markdown source) into [Play With Docker](http://labs.play-with-docker.com/) to see it in action.
+
+## Setup OpenFaaS
+
+    docker swarm init --advertise-addr $(hostname -i)
+    git clone https://github.com/alexellis/faas
+    cd faas
+    ./deploy_stack.sh
+
+## Check that one of the sample functions works
+
+    curl localhost:8080/function/func_echoit -d 'hello world'
+
+
+## Setup Kong
+
+    docker run -d --name kong-database \
+                  -p 5432:5432 \
+                  -e "POSTGRES_USER=kong" \
+                  -e "POSTGRES_DB=kong" \
+                  postgres:9.4
+
+    docker run --rm \
+        --link kong-database:kong-database \
+        -e "KONG_DATABASE=postgres" \
+        -e "KONG_PG_HOST=kong-database" \
+        kong:latest kong migrations up
+
+    docker run -d --name kong \
+        --link kong-database:kong-database \
+        -e "KONG_DATABASE=postgres" \
+        -e "KONG_PG_HOST=kong-database" \
+        -e "KONG_PROXY_ACCESS_LOG=/dev/stdout" \
+        -e "KONG_ADMIN_ACCESS_LOG=/dev/stdout" \
+        -e "KONG_PROXY_ERROR_LOG=/dev/stderr" \
+        -e "KONG_ADMIN_ERROR_LOG=/dev/stderr" \
+        -p 8000:8000 \
+        -p 8443:8443 \
+        -p 8001:8001 \
+        -p 8444:8444 \
+        kong:latest
+
+
+## Get a route to the OpenFaaS server
+
+    FAASTHOST=`hostname -i`
+
+
+## Put Kong in front of a single function
+
+    sleep 5   # wait for Kong to be ready
+
+    curl -i -X POST \
+      --url http://localhost:8001/apis/ \
+      --data 'name=echoit' \
+      --data 'uris=/echo' \
+      --data 'upstream_url=http://'$FAASTHOST':8080/function/func_echoit'
+
+    curl localhost:8000/echo -d 'hello there'
+
+## or put Kong in front of all the functions
+
+    curl -i -X POST \
+      --url http://localhost:8001/apis/ \
+      --data 'name=functions' \
+      --data 'uris=/functs' \
+      --data 'upstream_url=http://'$FAASTHOST':8080/function'
+
+    curl localhost:8000/functs/func_echoit -d 'hello there'
+
+
+## Add a some auth with a Kong plugin
+
+    curl -i -X POST \
+      --url http://localhost:8001/apis/echoit/plugins/ \
+      --data 'name=key-auth'
+
+    curl -i -X POST \
+      --url http://localhost:8001/consumers/ \
+      --data "username=jdoe"
+
+    curl -i -X POST \
+      --url http://localhost:8001/consumers/jdoe/key-auth/ \
+      --data 'key=longsecretkey'
+
+
+## Verify the plugin worked
+
+    curl localhost:8000/echo -d 'hello there'   # no key specified
+
+    curl localhost:8000/echo -d 'hello there' --header "apikey: badkey"
+
+    curl localhost:8000/echo -d 'hello there' --header "apikey: longsecretkey"