如何通过Docker命令行及Python库实现多容器实例的DNS解析

Great question! When you're using docker-compose to run multiple instances of a service, Docker's internal DNS lets tools like dig resolve the service name to all container IPs. Here's how you can replicate that using the Docker CLI and Python's Docker SDK:

Using Docker Command Line #

Method 1: Filter by docker-compose service label #

Docker-compose adds a label com.docker.compose.service=<your-service-name> to all containers belonging to a service. You can use this to filter containers and extract their IPs:

1. First, get the IDs of all containers for your service (replace my-service with your actual service name):

   docker ps -q -f "label=com.docker.compose.service=my-service"
   

2. Pipe those IDs into docker inspect to pull out the IP addresses. Replace <your-network-name> with the name of your docker-compose network (usually <project-name>_default, where <project-name> is your current directory name):

   docker inspect -f '{{.NetworkSettings.Networks.<your-network-name>.IPAddress}}' $(docker ps -q -f "label=com.docker.compose.service=my-service")
   

   If you don't know the network name, you can list all networks with docker network ls and look for one tied to your project. Alternatively, use a more generic command to output all IPs across any networks the containers are part of:

   docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}} {{end}}' $(docker ps -q -f "label=com.docker.compose.service=my-service")
   

Method 2: Use docker-compose directly #

If you're in the same directory as your docker-compose.yml, you can use docker-compose commands to simplify this:

docker-compose ps -q my-service | xargs docker inspect -f '{{.NetworkSettings.Networks.${COMPOSE_PROJECT_NAME}_default.IPAddress}}'

The COMPOSE_PROJECT_NAME environment variable automatically uses your current directory name (you can set it manually if needed).

Using Python's Docker SDK #

First, install the official Docker SDK for Python:

pip install docker

Option 1: Filter containers by docker-compose service label #

This works just like the CLI method, but programmatically:

import docker

# Initialize the Docker client (uses local daemon by default)
client = docker.from_env()

# Replace with your service name
TARGET_SERVICE = "my-service"

# Get all containers belonging to the target service
service_containers = client.containers.list(
    filters={"label": f"com.docker.compose.service={TARGET_SERVICE}"}
)

# Extract IP addresses (assuming containers use the default docker-compose network)
container_ips = []
for container in service_containers:
    # Iterate through the container's networks to find the project's default network
    for network_name, network_details in container.attrs["NetworkSettings"]["Networks"].items():
        if "_default" in network_name:
            container_ips.append(network_details["IPAddress"])
            break

print(f"IP addresses for service '{TARGET_SERVICE}':")
for ip in container_ips:
    print(f"- {ip}")

Option 2: Query a specific Docker network #

If you're using a custom named network, you can fetch all containers in that network and filter by service name:

import docker

client = docker.from_env()

# Replace with your custom network name and service container name prefix
TARGET_NETWORK = "my-custom-network"
SERVICE_NAME_PREFIX = "my-service"

# Get the target network object
network = client.networks.get(TARGET_NETWORK)

# Filter containers in the network that belong to your service
service_containers = [
    container for container in network.containers
    if SERVICE_NAME_PREFIX in container.name
]

# Extract IP addresses directly from the network context
container_ips = [
    container.attrs["NetworkSettings"]["Networks"][TARGET_NETWORK]["IPAddress"]
    for container in service_containers
]

print(f"IP addresses for service in network '{TARGET_NETWORK}':")
for ip in container_ips:
    print(f"- {ip}")

Both approaches give you the same list of IPs that dig returns internally, since we're directly querying Docker's container metadata.

内容的提问来源于stack exchange，提问作者JamesP