Good tech adventures start with some frustration, a need, or a requirement. This is the story of how I simplified the management and access of my local web applications with the help of Traefik and dnsmasq. The reasoning applies just as well for a production server using Docker.
My dev environment is composed of a growing number of web applications self-hosted on my laptop. Such applications include several websites, tools, editors, registries, … They use databases, REST APIs, or more complex backends. Take the example of Supabase, the Docker Compose file includes the Studio, the Kong API gateway, the authentication service, the REST service, the real-time service, the storage service, the meta service, and the PostgreSQL database.
The result is a growing number of containers started on my laptop, accessible at localhost
on various ports. Some of them use the default ports and cannot run in parallel to avoid conflicts. For example, the 3000
and 8000
ports are common to a lot of containers present on my machine. To circumvent the issue, some containers use custom ports which I often happen to forget.
The solution is to create local domain names which are easy to remember and use a web proxy to route the requests to the correct container. Traefik helps in the routing and the discovery of those services and dnsmasq provides a custom top-level domain (pseudo-TLD) to access them.
Another usage of Traefik is a production server using multiple Docker Compose files for various websites and web applications. The containers communicate inside an internal network and are exposed through a proxy service, in our case implemented with Caddy.
Problem description
Out of many, let’s take 3 web applications running locally. All of them are managed with Docker Compose:
- Adaltas website, 1 container, Gatsby-based static website
- Alliage website, 10 containers, Next.js frontend, Node.js backend, and Supabase
- Penpot, 6 containers, Penpot frontend, backend services plus Inbucket for email testing (personal addition)
By default, those containers expose the following ports on localhost:
- Adaltas
8000
Gatsby server in dev mode9000
Gatsby service to serve a build website
- Alliage
3000
Next.js website both dev and build mode3001
Node.js custom API3000
Supabase Studio5555
Supabase Meta8000
Kong HTTP8443
Kong HTTPS5432
PostgreSQL2500
Inbucket SMTP server9000
Inbucket Web interface1100
Inbucket POP3 server
- Penpot
2500
Inbucket SMTP server9000
Inbucket Web interface1100
Inbucket POP3 server9001
Penpot frontend
Note, depending on your environment and desires, some ports might be restricted while other ports might be accessible.
As you can see, many ports collide with each other. It is not just the 2 instances of Inbucket running in parallel. For example, port 8000
is used both by Gatsby and Kong. It is a common default port for several applications. The same goes for ports 3000
, 8080
, 8443
, …
One solution is to assign distinctive ports for each service. However, this approach is not scalable. Soon enough, I forget to which port each service is assigned.
Expected behavior
A better solution is the usage of a reverse proxy with hostnames easy to remember. Here is what we expect:
- Adaltas
www.adaltas.local
Gatsby server in dev modebuild.adaltas.local
Gatsby service to serve a build website
- Alliage
www.alliage.local
Next.js website both dev and build modeapi.alliage.local
Node.js custom APIstudio.alliage.local
Supabase Studiometa.alliage.local
Supabase Metakong.alliage.local
Kong HTTPkong.alliage.local
Kong HTTPSsql.alliage.local
PostgreSQLsmtp.alliage.local
Inbucket SMTP servermail.alliage.local
Inbucket Web interfacepop3.alliage.local
Inbucket POP3 server
- Penpot
www.penpot.local
Penpot frontendsmtp.penpot.local
Inbucket SMTP servermail.penpot.local
Inbucket Web interfacepop3.penpot.local
Inbucket POP3 server
In a traditional setting, the reverse proxy is configured with one or multiple configuration files with all the routing information. However, a central configuration is not so convenient. It is preferable to have each service declares which hostname they resolve.
Automatic routing registration
All my web services are managed with Docker Compose. Ideally, I expect information to be present inside the Docker Compose file. Traefik is cloud-native in the sense that it configures itself using cloud-native workflows. The application provides some instructions present in its docker-compose.yml
file and the containers are automatically exposed.
The way Traefik works with Docker, it plugs into the Docker socket, detects new services, and creates the routes for you.
Starting Traefik
To start Traefik inside Docker is straightforward (never say easy). The docker-compose.yml
file is:
version: '3'
services:
reverse-proxy:
image: traefik:v2.9
command: --api.insecure=true --providers.docker
ports:
- "80:80"
- "8080:8080"
volumes:
- /var/run/docker.sock:/var/run/docker.sock
Registering new services
Let’s consider an additional service. The Adaltas website is a single container based on Gatsby. In development mode, it starts a web server on port 8000
. I expect it to be accessible with the hostname www.adaltas.local
on port 80
.
Following the Traefik’s getting started with Docker, the integration is made with the property traefik.http.routers.router_name.rule
present in the labels
field of the docker service. It defines the hostname under which our website is accessible on port 80
. It is set to www.adaltas.localhost
because the .localhost
TLD resolves locally by default. Since I prefer to use the .local
domain, we set the domain to www.adaltas.local
later using dnsmasq. The traffic is then routed to the container IP on port 8000. The container port is obtained by Traefik from the Docker Compose’s ports
field.
version: '3'
services:
www:
container_name: adaltas-www
...
labels:
- "traefik.http.routers.adaltas-www.rule=Host(`www.adaltas.localhost`)"
ports:
- "8000:8000"
This works when both the Traefik and the Adaltas services are defined in the same Docker compose file. Firing docker-compose up
and you can:
http://localhost:8080
: Access the Traefik web UIhttp://localhost:8080/api/rawdata
: Access the Traefik’s API rawdatahttp://www.adaltas.localhost
: Access the Adaltas website in development modehttp://localhost:8080
: Same ashttp://www.adaltas.localhost
There are 3 limitations we need to deal with:
- Internal networking
It only works because all the services are declared inside the same Docker Compose file. With separated Docker Compose files, an internal network must be used to communicate between the Traefic container and the targetted containers. - Domain name
I wish to use a pseudo top-level domain (TLD), for example,www.adaltas.local
instead ofwww.adaltas.localhost
. The.local
TLD does not yet resolve locally, a local DNS server must be configured. - Port label
The port of Adaltas is defined inside the Docker Compose file. Thus, it is exposed on the host machine and it collides with other services. Port forwarding must be disabled and Traefik must be instructed about the port with another mechanism than theports
field.
Internal networking
When defined across separated files, the container cannot communicate. Each Docker Compose file generates a dedicated network. The targeted service is visible inside the Traefik UI. However, the request fails to be routed.
The containers must share a common network to communicate. When the Traefik container is started, a traefik_default
network is created, see docker network list
. Instead of creating a new network, let’s reuse it. Enrich the Docker Compose file of the targetted container, the Adaltas website in our case, with the network
field:
version: '3'
services:
www:
container_name: adaltas-www
networks: default: name: traefik_default
After starting the 2 Docker Compose setups with docker-compose up
, the Traefik and the Website containers start communicating.
Domain name
It is time to tackle the FQDN of our services. The current TLD in use, .localhost
, is perfectly fine. It works by default and it is officially reserved for this usage. However, I wish to use my own top-level domains (pseudo-TLD name), we’ll use .local
in this example.
Disclaimer, using a pseudo-TLD name is not recommended. The
.local
TLD is used by multicast DNS / zero-configuration networking. In practice, I haven’t encountered any issues. To mitigate the risk of conflicts, RFC 2606 reserves the following TLD names:.test
,.example
,.invalid
,.localhost
.
A local DNS server is used to resolve the *.local
addresses. I had some experience with Bind in the past. A simpler and more lightweight option is the usage of dnsmasq. The instructions below cover the installation on MacOS and Ubuntu Desktop. In both cases, dnsmaq is installed and configured to not interfere with the current DNS settings.
MacOS instructions:
brew install dnsmasq
mkdir -pv $(brew --prefix)/etc/
echo 'address=/.local/127.0.0.1' >> $(brew --prefix)/etc/dnsmasq.conf
sudo brew services start dnsmasq
sudo mkdir -v /etc/resolver
sudo bash -c 'echo "nameserver 127.0.0.1" > /etc/resolver/test'
scutil --dns
Linux instructions with NetworkManager (eg Ubuntu Desktop):
systemctl disable systemd-resolved
systemctl stop systemd-resolved
unlink /etc/resolv.conf
cat <<CONF | sudo tee /etc/NetworkManager/conf.d/00-use-dnsmasq.conf
[main]
dns=dnsmasq
CONF
cat <<CONF | sudo tee /etc/NetworkManager/dnsmasq.d/00-dns-public.conf
server=8.8.8.8
CONF
cat <<CONF | sudo tee /etc/NetworkManager/dnsmasq.d/00-address-local.conf
address=/.local/127.0.0.1
CONF
systemctl restart NetworkManager
Use dig
to validate that any FQDN using our pseudo-TLD resolves to the local
machine:
Port label
With the introduction of a reverse proxy like Traefik, exposing the container port on the host machine is no longer necessary, thus, eliminating the risk of collision between the exposed port and the ones of other services.
One label is already present to define the hostname of the website service. Traefik comes with a lot of complementary labels. The traefik.http.services.service_name.loadbalancer.server.port
property tells Traefik to use a specific port to connect to a container.
The final Docker Compose file looks like this:
version: '3'
services:
www:
container_name: adaltas-www
image: node:18
volumes:
- .:/app
user: node
working_dir: /app
command: bash -c "yarn install && yarn run develop"
labels:
- "traefik.http.routers.adaltas-www.rule=Host(`www.adaltas.local`)"
- "traefik.http.services.adaltas-www.loadbalancer.server.port=8000"
networks:
default:
name: traefik_default
Conclusion
With Traefik, I like the idea of my container services registering automatically in a cloud-native philosophy. It provided me with confort and simplicity. Also, dnsmasq has proved to be well-documented and quick to adjust to my various requirements.
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