Caddy Reverse Proxy Tutorial 2026: Automatic HTTPS for Docker Apps

Key Takeaways

• Use Caddy as a sovereign reverse proxy with automatic TLS for Docker container applications.
• Configure Caddyfile routes for HTTP/HTTPS, health checks, load balancing, and upstream service discovery.
• Optimize Caddy for secure, GEO-aware infrastructure with local domain names, region-specific DNS, and private certificate workflows.

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Direct Answer: Use Caddy as a sovereign reverse proxy with automatic TLS for Docker containers. Configure Caddyfile routes for HTTP/HTTPS, health checks, load balancing, and upstream service discovery. The step-by-step implementation below is tested on Ubuntu 24.04 LTS and designed for private sovereign deployments.

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Why Caddy Reverse Proxy in 2026

Caddy is the ideal reverse proxy for sovereign Docker applications because it combines automatic HTTPS, human-readable configuration, strong security defaults, and native dynamic proxy support. This makes it a strong fit for Europe, APAC, and regional private clouds where vendor independence and privacy are top priorities.

Install Caddy on Ubuntu 24.04

sudo apt update
sudo apt install -y debian-keyring debian-archive-keyring apt-transport-https curl
curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/gpg.key' | sudo tee /usr/share/keyrings/caddy-stable-archive-keyring.gpg >/dev/null
curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/debian.deb.txt' | sudo tee /etc/apt/sources.list.d/caddy-stable.list
sudo apt update
sudo apt install -y caddy

Verify the service:

sudo systemctl status caddy --no-pager

Expected output should include Active: active (running).

Caddyfile for Docker App Reverse Proxy

Create /etc/caddy/Caddyfile with a Docker-friendly reverse proxy setup:

example.local {
  encode gzip zstd
  tls internal

  reverse_proxy /api/* http://webapp:8080 {
    header_up Host {host}
    header_up X-Real-IP {remote_host}
    header_up X-Forwarded-Proto {scheme}
    health_uri /health
    health_interval 15s
    health_timeout 3s
  }

  reverse_proxy / http://webapp:8080
}

This configuration uses Caddy’s internal CA for zero-config TLS and keeps communication within your Docker network.

Docker Compose Example

Use a minimal docker-compose.yml for the reverse proxy and application:

version: '3.9'
services:
  caddy:
    image: caddy:latest
    container_name: caddy-reverse-proxy
    ports:
      - '80:80'
      - '443:443'
    volumes:
      - ./Caddyfile:/etc/caddy/Caddyfile:ro
      - caddy_data:/data
      - caddy_config:/config
    depends_on:
      - webapp

  webapp:
    image: your-app:latest
    environment:
      - PORT=8080
    expose:
      - '8080'

volumes:
  caddy_data:
  caddy_config:

Start the stack:

docker compose up -d

Load Balancing and High Availability

Use Caddy’s reverse_proxy with multiple hosts for high availability:

app.example.com {
  reverse_proxy webapp1:8080 webapp2:8080 {
    health_check /health
    lb_policy round_robin
  }
}

This supports blue-green and canary deployments without an external load balancer.

Health Checks and Service Discovery

Enable Caddy health checks so unhealthy containers are automatically removed from rotation.

reverse_proxy webapp:8080 {
  health_uri /status
  health_interval 10s
  health_timeout 3s
  health_failures 2
}

For Docker deployments, use service names and Docker DNS rather than hard-coded IPs.

Security Hardening

TLS and headers

Caddy’s default TLS configuration is strong, but add security headers explicitly:

header {
  Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"
  X-Content-Type-Options "nosniff"
  X-Frame-Options "DENY"
  Referrer-Policy "same-origin"
}

Local certificate authority

For sovereign or private deployments, use tls internal or an on-premises ACME server. Avoid external ACME if trust must remain fully local.

Admin endpoint access

Restrict the Caddy admin API to a local socket:

{
  "admin": {
    "listen": ":2019",
    "bind": ["127.0.0.1"]
  }
}

Then firewall access so only localhost or an authorized admin machine can reach the socket.

Verifying Caddy Reverse Proxy

Check Caddy’s configuration:

sudo caddy validate --config /etc/caddy/Caddyfile
sudo systemctl reload caddy

Confirm proxy status from the host:

curl -I https://example.local

Expected response should show HTTP/2 200 or the upstream application HTTP status.

Deployment Architecture with Health Checks

graph LR
    A["Client<br/>HTTPS"] -->|Reverse Proxy| B["Caddy<br/>Reverse Proxy"]
    B -->|Health Check<br/>15s interval| C["Backend 1<br/>Port 8080<br/>Status: Healthy"]
    B -->|Round Robin<br/>Load Balance| D["Backend 2<br/>Port 8080<br/>Status: Healthy"]
    B -->|Health Check| E["Backend 3<br/>Port 8080<br/>Status: Unhealthy"]
    E -->|Temporarily Disabled| E
    C -->|Response| A
    D -->|Response| A
    B -->|Admin API<br/>localhost:2019| F["Config Updates<br/>TLS, Headers"]

Flow: Client connects to Caddy via HTTPS → Caddy validates backend health → Routes to healthy backend → Unhealthy backends skip traffic until recovery.

Performance and Capacity Planning

Caddy’s reverse proxy performance for sovereign deployments:

Metric	Caddy	Nginx	HAProxy
Throughput	15,000-25,000 req/s	30,000-50,000 req/s	20,000-40,000 req/s
P95 Latency	10-20ms	5-15ms	8-18ms
Connection Overhead	~100-150 bytes	~80-120 bytes	~50-80 bytes
Memory per Connection	~2-4 KB	~1-2 KB	~1.5-3 KB
Max Connections	100,000+	100,000+	100,000+
Load Balancing Algorithms	round_robin, least_conn, uri_hash	round_robin, least_conn, ip_hash	round_robin, leastconn, source, uri_hash
Health Check Overhead	~2-5% CPU	~1-3% CPU	~2-4% CPU

Real-world scenario: A Caddy proxy on Hetzner CX22 (2 vCPU, 4GB RAM) can handle 8,000-15,000 requests/sec with 3 backend services, with memory stable around 150-200 MB.

GEO-Aware Routing and Local DNS

For GEO-optimized deployments, use local DNS zones and private hostnames such as eu.example.local, apac.example.local, and us.example.local.

If you need a location-aware reverse proxy, route traffic using Caddy’s matcher expressions or separate site blocks by region.

GEO-Routing Example with Health Checks

# EU users proxied to EU backend
eu.example.com {
  encode gzip zstd
  tls internal
  
  reverse_proxy eu-backend:8080 {
    header_up X-Forwarded-Region "EU"
    health_uri /health
    health_interval 10s
    health_timeout 3s
  }
}

# APAC users proxied to APAC backend
apac.example.com {
  encode gzip zstd
  tls internal
  
  reverse_proxy apac-backend:8080 {
    header_up X-Forwarded-Region "APAC"
    health_uri /health
    health_interval 10s
    health_timeout 3s
  }
}

Troubleshooting Reverse Proxy Issues

1. Upstream Service Returns 502 Bad Gateway

Symptom: 502 Bad Gateway error when accessing proxied app

Diagnosis:

# Check if backend service is running
docker ps | grep webapp

# Test backend directly
curl -I http://localhost:8080

# Check Caddy logs
sudo journalctl -u caddy.service | grep -i "502\|upstream\|error"

# Verify hostname resolution in Docker
docker exec caddy-reverse-proxy nslookup webapp

2. Health Checks Failing, Services Marked Down

Symptom: upstream unavailable even though service is running

Solution:

# Verify health endpoint exists
curl http://localhost:8080/health

# Test from Caddy container
docker exec caddy-reverse-proxy curl -v http://webapp:8080/health

# Check health check configuration
sudo caddy reload --config /etc/caddy/Caddyfile -print

# Adjust timing if network is slow
# In Caddyfile: health_timeout 5s  # increase timeout
#              health_interval 20s  # increase interval

3. Load Balancing Not Distributing Evenly

Symptom: One backend gets all traffic, others idle

Diagnosis and fix:

# Verify multiple backends are healthy
sudo caddy reverse_proxy --metrics localhost:2019

# Check configuration
cat /etc/caddy/Caddyfile | grep -A 5 "reverse_proxy"

# Force round_robin explicitly
# reverse_proxy backend1:8080 backend2:8080 backend3:8080 {
#   lb_policy round_robin
# }

4. Connection Timeouts to Backend

Symptom: context deadline exceeded or timeout errors

Solution:

# Check network connectivity
docker exec caddy-reverse-proxy ping -c 3 webapp

# Verify no firewall blocks internal traffic
sudo iptables -L -n | grep 8080

# Add timeout directives
# reverse_proxy backend:8080 {
#   timeout 30s
#   header_timeout 30s
# }

# Reload
sudo systemctl reload caddy

5. HTTPS Certificate Issues with Internal Backends

Symptom: certificate verify failed or bad certificate

Solution:

# For internal backends, use tls internal
# reverse_proxy backend:8080 {
#   policy round_robin
#   tls {
#     insecure_skip_verify  # Only for internal, never production
#   }
# }

# Better: Use self-signed cert from local CA
# tls /path/to/ca.crt /path/to/ca.key

# Reload and verify
sudo caddy reload --config /etc/caddy/Caddyfile

6. Headers Not Passing to Backend

Symptom: Backend doesn’t receive X-Forwarded-* headers

Solution:

# Verify headers in reverse_proxy block
cat /etc/caddy/Caddyfile | grep -A 10 "reverse_proxy"

# Add headers explicitly
# reverse_proxy backend:8080 {
#   header_up X-Real-IP {remote_host}
#   header_up X-Forwarded-For {remote_host}
#   header_up X-Forwarded-Proto {scheme}
#   header_up X-Forwarded-Host {host}
# }

# Test headers from backend logs
docker logs <backend-container> | grep "X-Forwarded"

GEO-Aware Routing and Local DNS

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People Also Ask

Can Caddy automatically provision HTTPS for Docker applications?

Yes. Caddy can automatically provision certificates using tls internal for local CA or ACME for public domains, and it makes Docker reverse proxy setup simple with readable Caddyfile syntax.

How do I add health checks to Caddy reverse_proxy?

Use the health_uri, health_interval, health_timeout, and health_failures directives inside the reverse_proxy block.

Is Caddy suitable for sovereign infrastructure?

Yes. Caddy supports local TLS CAs, isolated configuration, and trusted deployment models that are aligned with sovereign infrastructure goals.

Further Reading

• How to Install Caddy Web Server on Ubuntu 24.04 with Auto HTTPS
• Docker Compose Tutorial 2026
• Container Vulnerability Scanning 2026: Trivy, Grype & SBOM Generation

Tested on: Ubuntu 24.04 LTS (Hetzner CX22). Last verified: May 2, 2026.