跨主机连接两个Docker容器的可行方案咨询（已试Swarm/Weave未果）

Hey there! Sorry to hear you've hit snags with Docker Swarm and Weave when trying to connect your web container on Host A to the DB container on Host B. Let's break down some reliable, actionable solutions that should get things working:

If you need a fast, no-frills solution, this is the way to go—great for testing or small setups:

• On Host B, start your DB container with a port mapped to Host B's internal or public IP (stick to internal if possible for security). For example, with PostgreSQL:

  docker run -d -p <HostB_INTERNAL_IP>:5432:5432 --name my-db -e POSTGRES_PASSWORD=yoursecurepassword postgres
  

• On Host A, configure your web app to connect to <HostB_INTERNAL_IP>:5432 instead of a container name.
• Critical Checks: Make sure Host A and Host B can reach each other over the network (test with ping <HostB_INTERNAL_IP>) and that your firewall/security group allows incoming traffic on the DB port (5432 in this example).
• Pro Tip: Avoid exposing the DB port to the public internet if you can—use your internal network or a VPN for remote setups.

Chances are your earlier Swarm attempt failed due to missing port openings or incorrect network configuration. Here's the step-by-step correct setup:

1. Initialize Swarm on Host A:

   docker swarm init --advertise-addr <HostA_INTERNAL_IP>
   

   Copy the docker swarm join command that's output—you'll need it for Host B.
2. Join Host B to the Swarm:
   Run the copied join command on Host B (it'll look like this, with your unique token):

   docker swarm join --token SWMTKN-1-xxxxxx <HostA_INTERNAL_IP>:2377
   

3. Create an Attachable Overlay Network:
   This lets standalone containers (not just Swarm services) connect to the network:

   docker network create --driver overlay --attachable cross-host-net
   

4. Launch Containers on the Network:
   • On Host A: docker run -d --name my-web --network cross-host-net your-web-image
   • On Host B: docker run -d --name my-db --network cross-host-net your-db-image
5. Test the Connection:
   Inside your web container, you can now connect to the DB using the container name my-db (Swarm's overlay network handles service discovery automatically).

• Why You Might Have Failed Before: Ensure these ports are open on both hosts:
  • 2377 (Swarm management)
  • 7946 (node-to-node communication)
  • 4789 (overlay network data traffic)

Perfect if you're working across cloud providers or remote machines without a dedicated internal network:

• Install Tailscale (or WireGuard) on both Host A and Host B. Once logged in, both hosts will be part of a secure virtual network with unique internal IPs.
• You can either:
  • Use the port mapping method above, but replace Host B's IP with its Tailscale virtual IP.
  • Or, for a cleaner setup, create a bridge network on each host and use Tailscale to forward the DB container's port to Host A (though port mapping is simpler for most cases).
• The best part? No complex network config—Tailscale handles encryption and routing out of the box.

For larger, distributed systems where you need service discovery and encrypted connections:

• Deploy a Consul agent on both Host A and Host B to form a small Consul cluster.
• Configure Docker Connect to register your web and DB containers as services in Consul.
• Your web container can then access the DB using its Consul service name, and Connect will automatically establish a secure, encrypted connection between the two containers across hosts.
• This is overkill for simple setups, but ideal if you're scaling to more containers or hosts.

Quick Troubleshooting Tips #

Before diving into any solution, confirm:

• Host A can ping Host B and vice versa.
• You can telnet to the DB port from Host A: telnet <HostB_IP> <DB_PORT>—if this fails, your firewall is blocking traffic.
• Check container logs with docker logs my-web or docker logs my-db to see specific connection errors (e.g., "connection refused" vs "timeout").

内容的提问来源于stack exchange，提问作者Rakesh Sivagouni