233 lines
9.3 KiB
Markdown
233 lines
9.3 KiB
Markdown
# Docker & Traefik
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In this use case, we want to use Traefik as a _layer-7_ load balancer with SSL termination for a set of micro-services used to run a web application.
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We also want to automatically _discover any services_ on the Docker host and let Traefik reconfigure itself automatically when containers get created (or shut down) so HTTP traffic can be routed accordingly.
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In addition, we want to use Let's Encrypt to automatically generate and renew SSL certificates per hostname.
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## Setting Up
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In order for this to work, you'll need a server with a public IP address, with Docker installed on it.
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In this example, we're using the fictitious domain _my-awesome-app.org_.
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In real-life, you'll want to use your own domain and have the DNS configured accordingly so the hostname records you'll want to use point to the aforementioned public IP address.
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## Networking
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Docker containers can only communicate with each other over TCP when they share at least one network.
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This makes sense from a topological point of view in the context of networking, since Docker under the hood creates IPTable rules so containers can't reach other containers _unless you'd want to_.
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In this example, we're going to use a single network called `web` where all containers that are handling HTTP traffic (including Traefik) will reside in.
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On the Docker host, run the following command:
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```shell
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docker network create web
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```
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Now, let's create a directory on the server where we will configure the rest of Traefik:
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```shell
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mkdir -p /opt/traefik
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```
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Within this directory, we're going to create 3 empty files:
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```shell
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touch /opt/traefik/docker-compose.yml
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touch /opt/traefik/acme.json && chmod 600 /opt/traefik/acme.json
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touch /opt/traefik/traefik.toml
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```
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The `docker-compose.yml` file will provide us with a simple, consistent and more importantly, a deterministic way to create Traefik.
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The contents of the file is as follows:
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```yaml
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version: '2'
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services:
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traefik:
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image: traefik:1.3.5
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restart: always
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ports:
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- 80:80
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- 443:443
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networks:
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- web
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volumes:
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- /var/run/docker.sock:/var/run/docker.sock
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- /srv/traefik/traefik.toml:/traefik.toml
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- /srv/traefik/acme.json:/acme.json
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container_name: traefik
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networks:
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web:
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external: true
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```
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As you can see, we're mounting the `traefik.toml` file as well as the (empty) `acme.json` file in the container.
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Also, we're mounting the `/var/run/docker.sock` Docker socket in the container as well, so Traefik can listen to Docker events and reconfigure it's own internal configuration when containers are created (or shut down).
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Also, we're making sure the container is automatically restarted by the Docker engine in case of problems (or: if the server is rebooted).
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We're publishing the default HTTP ports `80` and `443` on the host, and making sure the container is placed within the `web` network we've created earlier on.
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Finally, we're giving this container a static name called `traefik`.
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Let's take a look at a simple `traefik.toml` configuration as well before we'll create the Traefik container:
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```toml
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debug = false
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checkNewVersion = true
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logLevel = "ERROR"
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defaultEntryPoints = ["https","http"]
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[entryPoints]
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[entryPoints.http]
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address = ":80"
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[entryPoints.http.redirect]
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entryPoint = "https"
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[entryPoints.https]
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address = ":443"
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[entryPoints.https.tls]
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[retry]
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[docker]
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endpoint = "unix:///var/run/docker.sock"
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domain = "my-awesome-app.org"
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watch = true
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exposedbydefault = false
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[acme]
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email = "your-email-here@my-awesome-app.org"
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storage = "acme.json"
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entryPoint = "https"
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OnHostRule = true
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```
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This is the minimum configuration required to do the following:
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- Log `ERROR`-level messages (or more severe) to the console, but silence `DEBUG`-level messagse
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- Check for new versions of Traefik periodically
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- Create two entry points, namely an `HTTP` endpoint on port `80`, and an `HTTPS` endpoint on port `443` where all incoming traffic on port `80` will immediately get redirected to `HTTPS`.
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- Enable the Docker configuration backend and listen for container events on the Docker unix socket we've mounted earlier. However, **new containers will not be exposed by Traefik by default, we'll get into this in a bit!**
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- Enable automatic request and configuration of SSL certificates using Let's Encrypt.
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These certificates will be stored in the `acme.json` file, which you can back-up yourself and store off-premises.
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Alright, let's boot the container. From the `/opt/traefik` directory, run `docker-compose up -d` which will create and start the Traefik container.
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## Exposing Web Services to the Outside World
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Now that we've fully configured and started Traefik, it's time to get our applications running!
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Let's take a simple example of a micro-service project consisting of various services, where some will be exposed to the outside world and some will not.
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The `docker-compose.yml` of our project looks like this:
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```yaml
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version: "2.1"
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services:
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app:
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image: my-docker-registry.com/my-awesome-app/app:latest
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depends_on:
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db:
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condition: service_healthy
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redis:
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condition: service_healthy
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restart: always
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networks:
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- web
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- default
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expose:
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- "9000"
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labels:
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- "traefik.backend=my-awesome-app-app"
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- "traefik.docker.network=web"
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- "traefik.frontend.rule=Host:app.my-awesome-app.org"
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- "traefik.enable=true"
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- "traefik.port=9000"
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db:
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image: my-docker-registry.com/back-end/5.7
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restart: always
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redis:
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image: my-docker-registry.com/back-end/redis:4-alpine
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restart: always
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events:
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image: my-docker-registry.com/my-awesome-app/events:latest
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depends_on:
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db:
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condition: service_healthy
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redis:
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condition: service_healthy
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restart: always
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networks:
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- web
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- default
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expose:
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- "3000"
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labels:
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- "traefik.backend=my-awesome-app-events"
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- "traefik.docker.network=web"
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- "traefik.frontend.rule=Host:events.my-awesome-app.org"
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- "traefik.enable=true"
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- "traefik.port=3000"
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networks:
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web:
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external: true
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```
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Here, we can see a set of services with two applications that we're actually exposing to the outside world.
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Notice how there isn't a single container that has any published ports to the host -- everything is routed through Docker networks.
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Also, only the containers that we want traffic to get routed to are attached to the `web` network we created at the start of this document.
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Since the `traefik` container we've created and started earlier is also attached to this network, HTTP requests can now get routed to these containers.
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### Labels
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As mentioned earlier, we don't want containers exposed automatically by Traefik.
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The reason behind this is simple: we want to have control over this process ourselves.
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Thanks to Docker labels, we can tell Traefik how to create it's internal routing configuration.
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Let's take a look at the labels themselves for the `app` service, which is a HTTP webservice listing on port 9000:
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```yaml
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- "traefik.backend=my-awesome-app-app"
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- "traefik.docker.network=web"
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- "traefik.frontend.rule=Host:app.my-awesome-app.org"
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- "traefik.enable=true"
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- "traefik.port=9000"
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```
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First, we specify the `backend` name which corresponds to the actual service we're routing **to**.
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We also tell Traefik to use the `web` network to route HTTP traffic to this container.
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With the `frontend.rule` label, we tell Traefik that we want to route to this container if the incoming HTTP request contains the `Host` `app.my-awesome-app.org`.
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Essentially, this is the actual rule used for Layer-7 load balancing.
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With the `traefik.enable` label, we tell Traefik to include this container in it's internal configuration.
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Finally but not unimportantly, we tell Traefik to route **to** port `9000`, since that is the actual TCP/IP port the container actually listens on.
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#### Gotchas and tips
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- Always specify the correct port where the container expects HTTP traffic using `traefik.port` label.
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If a container exposes multiple ports, Traefik may forward traffic to the wrong port.
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Even if a container only exposes one port, you should always write configuration defensively and explicitly.
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- Should you choose to enable the `exposedbydefault` flag in the `traefik.toml` configuration, be aware that all containers that are placed in the same network as Traefik will automatically be reachable from the outside world, for everyone and everyone to see.
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Usually, this is a bad idea.
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- With the `traefik.frontend.auth.basic` label, it's possible for Traefik to provide a HTTP basic-auth challenge for the endpoints you provide the label for.
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- Traefik has built-in support to automatically export [Prometheus](https://prometheus.io) metrics
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- Traefik supports websockets out of the box. In the example above, the `events`-service could be a NodeJS-based application which allows clients to connect using websocket protocol.
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Thanks to the fact that HTTPS in our example is enforced, these websockets are automatically secure as well (WSS)
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### Final thoughts
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Using Traefik as a Layer-7 load balancer in combination with both Docker and Let's Encrypt provides you with an extremely flexible, powerful and self-configuring solution for your projects.
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With Let's Encrypt, your endpoints are automatically secured with production-ready SSL certificates that are renewed automatically as well.
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