Exposing Services with Traefik on Docker Swarm¶

This guide will help you expose your services securely through Traefik Proxy using Docker Swarm. We'll cover routing HTTP and HTTPS traffic, implementing TLS, adding middlewares, Let's Encrypt integration, and sticky sessions.

Prerequisites¶

Docker Swarm cluster initialized
Basic understanding of Docker Swarm concepts
Traefik deployed using the Traefik Docker Swarm Setup guide

Expose Your First HTTP Service¶

Let's expose a simple HTTP service using the whoami application. This will demonstrate basic routing to a backend service.

First, update your existing docker-compose.yml file if you haven't already:

services:
  whoami:
    image: traefik/whoami
    networks:
      - traefik_proxy
    deploy:
      replicas: 3
      labels:
        - "traefik.enable=true"
        - "traefik.http.routers.whoami.rule=Host(`whoami.swarm.localhost`)"
        - "traefik.http.routers.whoami.entrypoints=web,websecure"

Save this as docker-compose.yml and deploy the stack:

docker stack deploy -c docker-compose.yml traefik

Verify Your Service¶

Your service is now available at http://whoami.swarm.localhost/. Test that it works:

curl -H "Host: whoami.swarm.localhost" http://localhost/

You should see output similar to:

Hostname: whoami.1.7c8f7tr56q3p949rscxrkp80e
IP: 127.0.0.1
IP: ::1
IP: 10.0.1.8
IP: fe80::215:5dff:fe00:c9e
RemoteAddr: 10.0.1.2:45098
GET / HTTP/1.1
Host: whoami.swarm.localhost
User-Agent: curl/7.68.0
Accept: */*
Accept-Encoding: gzip
X-Forwarded-For: 10.0.1.1
X-Forwarded-Host: whoami.swarm.localhost
X-Forwarded-Port: 80
X-Forwarded-Proto: http
X-Forwarded-Server: 5789f594e7d5
X-Real-Ip: 10.0.1.1

This confirms that Traefik is successfully routing requests to your whoami application.

Add Routing Rules¶

Now we'll enhance our routing by directing traffic to different services based on URL paths. This is useful for API versioning, frontend/backend separation, or organizing microservices.

Update your docker-compose.yml to add another service:

# ...

# New service
  whoami-api:
    image: traefik/whoami
    networks:
      - traefik_proxy
    environment:
      - WHOAMI_NAME=API Service
    deploy:
      replicas: 2
      labels:
        - "traefik.enable=true"
        # Path-based routing
        - "traefik.http.routers.whoami-api.rule=Host(`whoami.swarm.localhost`) && PathPrefix(`/api`)"
        - "traefik.http.routers.whoami-api.entrypoints=web,websecure"
        - "traefik.http.routers.whoami-api.service=whoami-api-svc"
        - "traefik.http.services.whoami-api-svc.loadbalancer.server.port=80"

# ...

Apply the changes:

docker stack deploy -c docker-compose.yml traefik

Test the Path-Based Routing¶

Verify that different paths route to different services:

# Root path should go to the main whoami service
curl -H "Host: whoami.swarm.localhost" http://localhost/

# /api path should go to the whoami-api service
curl -H "Host: whoami.swarm.localhost" http://localhost/api

For the /api requests, you should see the response showing "API Service" in the environment variables section, confirming that your path-based routing is working correctly.

Enable TLS¶

Let's secure our service with HTTPS by adding TLS. We'll start with a self-signed certificate for local development.

Create a Self-Signed Certificate¶

Generate a self-signed certificate and dynamic config file to tell Traefik where the cert lives:

mkdir -p certs

# key + cert (valid for one year)
openssl req -x509 -nodes -days 365 -newkey rsa:2048 \
  -keyout certs/local.key -out certs/local.crt \
  -subj "/CN=*.swarm.localhost"

# dynamic config that tells Traefik where the cert lives
cat > certs/tls.yml <<'EOF'
tls:
  certificates:
    - certFile: /certificates/local.crt
      keyFile:  /certificates/local.key
EOF

Create a Docker config for the certificate files:

docker config create swarm-cert.crt certs/local.crt
docker config create swarm-cert.key certs/local.key
docker config create swarm-tls.yml certs/tls.yml

Update your docker-compose.yml file with the following changes:

# Add to the Traefik command section:
command:
  # ... existing commands ...
  - "--entryPoints.websecure.address=:443"
  - "--entryPoints.websecure.http.tls=true"
  - "--providers.file.directory=/etc/traefik/dynamic"

# Add to the root of your docker-compose.yml file:
configs:
  swarm-cert.crt:
    file: ./certs/local.crt
  swarm-cert.key:
    file: ./certs/local.key
  swarm-tls.yml:
    file: ./certs/tls.yml

Deploy the stack:

docker stack deploy -c docker-compose.yml traefik

Your browser can access https://whoami.swarm.localhost/ for the service. You'll need to accept the security warning for the self-signed certificate.

Add Middlewares¶

Middlewares allow you to modify requests or responses as they pass through Traefik. Let's add two useful middlewares: Headers for security and IP allowlisting for access control.

Add the following labels to your whoami service deployment section in docker-compose.yml:

deploy:
  # ... existing configuration ...
  labels:
    # ... existing labels ...

    # Secure Headers Middleware
    - "traefik.http.middlewares.secure-headers.headers.frameDeny=true"
    - "traefik.http.middlewares.secure-headers.headers.sslRedirect=true"
    - "traefik.http.middlewares.secure-headers.headers.browserXssFilter=true"
    - "traefik.http.middlewares.secure-headers.headers.contentTypeNosniff=true"
    - "traefik.http.middlewares.secure-headers.headers.stsIncludeSubdomains=true"
    - "traefik.http.middlewares.secure-headers.headers.stsPreload=true"
    - "traefik.http.middlewares.secure-headers.headers.stsSeconds=31536000"

    # IP Allowlist Middleware
    - "traefik.http.middlewares.ip-allowlist.ipallowlist.sourceRange=127.0.0.1/32,192.168.0.0/16,10.0.0.0/8"

    # Apply the middlewares
    - "traefik.http.routers.whoami.middlewares=secure-headers,ip-allowlist"

Add the same middleware to your whoami-api service:

deploy:
  # ... existing configuration ...
  labels:
    # ... existing labels ...
    - "traefik.http.routers.whoami-api.middlewares=secure-headers,ip-allowlist"

Apply the changes:

docker stack deploy -c docker-compose.yml traefik

Test the Middlewares¶

Now let's verify that our middlewares are working correctly:

Test the Secure Headers middleware:

curl -k -I -H "Host: whoami.swarm.localhost" https://localhost/

In the response headers, you should see security headers set by the middleware:

X-Frame-Options: DENY
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Strict-Transport-Security with the appropriate settings

Test the IP Allowlist middleware:

If your request comes from an IP that's in the allow list (e.g., 127.0.0.1), it should succeed:

curl -k -I -H "Host: whoami.swarm.localhost" https://localhost/

If you try to access from an IP not in the allow list, the request will be rejected with a 403 Forbidden response. To simulate this in a local environment, you can modify the middleware configuration temporarily to exclude your IP address, then test again.

Generate Certificates with Let's Encrypt¶

Let's Encrypt provides free, automated TLS certificates. Let's configure Traefik to automatically obtain and renew certificates for our services.

Instead of using self-signed certificates, update your existing docker-compose.yml file with the following changes:

Add the Let's Encrypt certificate resolver to the Traefik service command section:

command:
  # ... existing commands ...
  # Let's Encrypt configuration
  - "[email protected]" # replace with your actual email
  - "--certificatesresolvers.le.acme.storage=/letsencrypt/acme.json"
  - "--certificatesresolvers.le.acme.httpchallenge.entrypoint=web"

Add a volume for Let's Encrypt certificates:

volumes:
  # ...Existing volumes...
  - letsencrypt:/letsencrypt

Update your service labels to use the certificate resolver:

labels:
  # ... existing labels ...
  - "traefik.http.routers.whoami.tls.certresolver=le"

Do the same for any other services you want to secure:

labels:
  # ... existing labels ...
  - "traefik.http.routers.whoami-api.tls.certresolver=le"

Create a named volume for storing Let's Encrypt certificates by adding to the volumes section:

volumes:
  # ... existing volumes ...
  letsencrypt:
    driver: local

Apply the changes:

docker stack deploy -c docker-compose.yml traefik

Public DNS Required

Let's Encrypt may require a publicly accessible ___domain to validate ___domain ownership. For testing with local domains like whoami.swarm.localhost, the certificate will remain self-signed. In production, replace it with a real ___domain that has a publicly accessible DNS record pointing to your Traefik instance.

Once the certificate is issued, you can verify it:

# Verify the certificate chain
curl -v https://whoami.swarm.localhost/ 2>&1 | grep -i "server certificate"

You should see that your certificate is issued by Let's Encrypt.

Configure Sticky Sessions¶

Sticky sessions ensure that a user's requests always go to the same backend server, which is essential for applications that maintain session state. Let's implement sticky sessions for our whoami service.

Docker Swarm already has multiple replicas running; we'll now add sticky session configuration. Update your whoami service in the docker-compose.yml file:

Add Sticky Session Configuration¶

Add the following labels to your whoami service in the docker-compose.yml file:

deploy:
  # ... existing configuration ...
  labels:
    # ... existing labels ...

    # Sticky Sessions Configuration
    - "traefik.http.services.whoami.loadbalancer.sticky.cookie=true"
    - "traefik.http.services.whoami.loadbalancer.sticky.cookie.name=sticky_cookie"
    - "traefik.http.services.whoami.loadbalancer.sticky.cookie.secure=true"
    - "traefik.http.services.whoami.loadbalancer.sticky.cookie.httpOnly=true"

Apply the changes:

docker stack deploy -c docker-compose.yml traefik

Test Sticky Sessions¶

You can test the sticky sessions by making multiple requests and observing that they all go to the same backend container:

# First request - save cookies to a file
curl -k -c cookies.txt -H "Host: whoami.swarm.localhost" https://localhost/

# Subsequent requests - use the cookies
curl -k -b cookies.txt -H "Host: whoami.swarm.localhost" https://localhost/
curl -k -b cookies.txt -H "Host: whoami.swarm.localhost" https://localhost/

Pay attention to the Hostname field in each response - it should remain the same across all requests when using the cookie file, confirming that sticky sessions are working.

For comparison, try making requests without the cookie:

# Requests without cookies should be load-balanced across different containers
curl -k -H "Host: whoami.swarm.localhost" https://localhost/
curl -k -H "Host: whoami.swarm.localhost" https://localhost/

You should see different Hostname values in these responses, as each request is load-balanced to a different container.

Browser Testing

When testing in browsers, you need to use the same browser session to maintain the cookie. The cookie is set with httpOnly and secure flags for security, so it will only be sent over HTTPS connections and won't be accessible via JavaScript.

For more advanced configuration options, see the reference documentation.

Conclusion¶

In this guide, you've learned how to:

Expose HTTP services through Traefik in Docker Swarm
Set up path-based routing to direct traffic to different backend services
Secure your services with TLS using self-signed certificates
Add security with middlewares like secure headers and IP allow listing
Automate certificate management with Let's Encrypt
Implement sticky sessions for stateful applications

These fundamental capabilities provide a solid foundation for exposing any application through Traefik Proxy in Docker Swarm. Each of these can be further customized to meet your specific requirements.

Next Steps¶

Now that you understand the basics of exposing services with Traefik Proxy, you might want to explore:

Advanced routing options like query parameter matching, header-based routing, and more
Additional middlewares for authentication, rate limiting, and request modifications
Observability features for monitoring and debugging your Traefik deployment
TCP services for exposing TCP services
UDP services for exposing UDP services
Docker provider documentation for more details about the Docker integration