Introduction
When running containers directly with docker, one has to bear up with ports and networking directly. Actual environments make use of API Gateways, enabling API versioning and other standard features. One cannot achieve this out of the box with docker, but one may think of spinning a nginx/envoy proxy and configuring it to achieve the same feel. But that sounds like quite an overhead as one has to manually update configs for every new container being launched.
Traefik is a leading modern reverse proxy and load balancer that makes deploying microservices easy. Traefik integrates with your existing infrastructure components and configures itself automatically and dynamically.
How can Traefik help here??
Traefik supports discovery for both Docker and Docker Swarm. One simply needs to attach labels to their docker containers to configure Traefik. It provides a very simplified dashboard. One simply needs to be aware of key concepts to understand Traefik.
Understanding Traefik
There are three components:-
- Entrypoints
- Routers
- Rules
- Middlewares
- Service
Request will first hit the endpoints (Ports/Endpoints exposed by Traefik). Then the request will move to the routers, which further consists of rules and middlewares. A rule can be as simple as checking for prefix /hello. Next the accepted request will move to middlewares, which can be chained. Middlewares tweak the request before they are sent to service (Final Destination). For example we may want to strip the suffix /hello before our request is sent to our service. Services can be simply combination of a runnning container’s IP and port.
We will be configuring the above components by attaching labels to our containers.
Deploying an API and versioning it with Traefik
We will be deploying an application that takes a value from env variable APIVERSION and returns it to the user stating that it’s the application’s API Version. The application by default run on port 8080. Varying this variable will give the feel of deploying various API versions.
Requirements
- Docker - Building and running containers
- Docker Compose - Running Traefik
- curl - Verifying the APIs
- sed - String manipulation and substitution
- 2 Free Ports - docker-compose.yaml uses 8080 and 8081, if already in use please substitute them
Building the API container
We need to build the container image for this API
git clone https://github.com/crazystylus/Docker-Traefik-Discovery.git
cd Docker-Traefik-Discovery
docker build . -t myapi:v1
Configuring the labels
Below is are the labels generated by the script for apiversion 3.
traefik.enable=true
traefik.http.routers.myapi3.entrypoints=http
traefik.http.routers.myapi3.rule=PathPrefix(`/myapi/v3{regex:11805|/.*}`)
traefik.http.routers.myapi3.middlewares=myapi3-strip
traefik.http.middlewares.myapi3-strip.stripprefix.prefixes=/myapi/v3
Understanding what’s happening here ?!?
In the first label we are mentioning that we want this application to be discovered by Traefik.
Next we want our requests to enter from an entrypoint named http, which actually points to localhost:8081 as per the docker-compose file.
Then we are using creating a rule which checks for prefix /myapi/v3. Only the requests which satisfy this rule will move forward to middleware.
Now we are using a strip prefix middleware to remove /myapi/v3 from our request. We don’t need to specify the end service name, Traefik will automatically route it to our service.
Generating the labels dynamically
We can use the script below to dynamically generate labels. We just need to run export APIVERSION=x, where x represents the API version we want and then run the script below.
#!/bin/bash
echo "
traefik.enable=true
traefik.http.routers.myapi${APIVERSION}.entrypoints=http
traefik.http.routers.myapi${APIVERSION}.rule=PathPrefix(\`/myapi/v${APIVERSION}{regex:$$|/.*}\`)
traefik.http.routers.myapi${APIVERSION}.middlewares=myapi${APIVERSION}-strip
traefik.http.middlewares.myapi${APIVERSION}-strip.stripprefix.prefixes=/myapi/v${APIVERSION}" | sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/ -l /g'
NOTE sed command simply replaces newline with -l option used to set label in docker command
Testing the container
Run the below command and try opening http://localhost:8080, it should show the API Version as 9
export APIVERSION=9; docker run -it $(./labels.sh) -e APIVERSION=${APIVERSION} --rm -p 9090:8080 myapi:v1
Getting Traefik up and running
It’s very easy to configure and run traefik. You can simply do a docker-compose up to bring Traefik up
docker-compose up -d traefik
Spawning APIs
We will put a for loop and spawn some various API versions.
for APIVERSION in {1..6};
do
export APIVERSION; docker run -d $(./labels.sh) -e APIVERSION=${APIVERSION} -p 8080 --rm myapi:v1;
done;
Next we will open the Traefik dashboard at http://localhost:8080 and see the discovered containers. Next we can try hitting the containers To send traffic we just need to send traffic to http://localhost:8081 with correct path to access the correct API Version. For example to open API V2 one can access http://localhost:8081/myapi/v2/
To check all running APIs we can run curl in a for loop
for i in {1..6};
do
curl http://localhost:8081/myapi/v${i}/
done
NOTE Be sure to check that by mistake { } are not being escaped by the shell else substitution of ${i} with APIVERSION won’t happen in the curl command
Cleaning up the containers
Removing the 6 APIs we created
docker rm -f $(docker ps --filter "ancestor=myapi:v1" -q)
NOTE This will remove all containers running the image myapi:v1 which build and used in this demo
Stopping Traefik
docker-compose down
NOTE For this to work you need to be present in the folder with docker-compose.yaml
LINK TO GIT REPO https://github.com/crazystylus/Docker-Traefik-Discovery