If I know a Docker container IP address, I can easily communicate with it from another container, but as long as they are in same network.
My question is, how can I communicate with containers from another network and why can't I access local IP which is on the same machine? I am interested in network explanation why I can access 172.19.0.1 from 172.19.0.2 but I can't access 172.20.0.1 from 172.19.0.2.
What are possible workarounds to making Docker container from one network to communicate with docker container from another network?
You can publish a port and then access that port over localhost (or 0.0.0.0 for troubleshooting).
Other than that you could use an alternative to docker network like linking or other things. But I wouldn't suggest that. If you want two containers to communicate with eachother and not the public just create a new network for those two containers.
You can specify that this network is external and they can join it even from different compose files.
Related
I'm trying to better understand docker networking, but I'm confused by the following:
I spin up 2 contains via docker-compose (client, api). When I do this, a new network is created, myapp_default, and each container joins this network. The network is a bridge network, and it's at 172.18.0.1. The client is at 172.18.0.2 and the api is at 172.18.0.3.
I can now access the client at 172.18.0.2:8080 and the api at 172.18.0.3:3000 -- this makes total sense. I'm confused when I publish ports in docker-compose: 8080:8080 on the client, and 3000:3000 on the api.
Now I can access the containers from:
Client at 172.18.0.1:8080, 172.18.0.2:8080, and on the docker0 network at 172.17.0.1:8080
API at 172.18.0.1:3000, 172.18.0.3:8080, and on the docker0 network at 172.17.0.1:3000
1) Why can I access the client and api via the docker0 network when I publish ports?
2) Why can I connect to containers via 172.17.0.1 and 172.18.0.1 at all?
You can only access the container-private IP addresses because you're on the same native-Linux host as the Docker daemon. This doesn't work in any other environment (different hosts, MacOS or Windows hosts, environments like Docker Toolbox where Docker is in a VM) and even using docker inspect to find these IP addresses usually isn't a best practice.
When you publish ports they are accessible on the host at those ports. This does work in every environment (in Docker Toolbox "the host" is the VM) and is the recommended way to access your containers from outside Docker space. Unless you bind to a specific address, the containers are accessible on every host interface and every host IP address; that includes the artificial 172.17.0.1 etc. that get created with Docker bridge networks.
Publishing ports is in addition to the other networking-related setup Docker does; it doesn't prevent you from reaching the containers by other paths.
If you haven't yet, you should also read Networking in Compose in the Docker documentation. Whether you publish ports or not, you can use the names in the docker-compose.yml file like client and api as host names, connecting the the (unmapped) port the actual server processes are listening on. Between this functionality and what you get from publishing ports you don't ever actually need to directly know the container-private IP addresses.
I'm deploying a stack of services through the command:
docker stack deploy -c <docker-compose.yml> <stack-name>
And I'm mapping ports of one of these services on docker compose with ports: 8000:8000.
The network driver being used is overlay.
I can access these services via localhost:8000, via Peers IP(?).
When I inspect the network created, I can see the local IPs of each container (for instance, 10.0.1.2). But Where is the external IP of container (the one like 172.0. ...) ?
I am running these docker container on a virtual machine ubuntu.
How can I access the services running on containers from other nodes running on other networks? Isn't possible to access via hostIP:port?
If so, how do I get the host IP? When I do docker-machine IP I get "host is not running".
[EDIT: I wasn't doing port mapping between the host and the VM in virtualbox. Now it works!]
Whats the best way to communicate between containers on the same swarm?
Thanks
Whats the best way to communicate between containers on the same swarm? Through name discovery?
In general if you communicate between containers you should use the container/service name.
And for your other problem you probably wan't a reverse proxy like nginx or traefik.
i want to expose the container ip to the external network where the host is running so that i can directly ping the docker container ip from an external machine.
If i ping the docker container ip from the external machine where the machine hosting the docker and the machine from which i am pinging are in the same network i need to get the response from these machines
Pinging the container's IP (i.e. the IP it shows when you look at docker inspect [CONTAINER]) from another machine does not work. However, the container is reachable via the public IP of its host.
In addition to Borja's answer, you can expose the ports of Docker containers by adding -p [HOST_PORT]:[CONTAINER_PORT] to your docker run command.
E.g. if you want to reach a web server in a Docker container from another machine, you can start it with docker run -d -p 80:80 httpd:alpine. The container's port 80 is then reachable via the host's port 80. Other machines on the same network will then also be able to reach the webserver in this container (depending on Firewall settings etc. of course...)
Since you tagged this as kubernetes:
You cannot directly send packets to individual Docker containers. You need to send them to somewhere else that’s able to route them. In the case of plain Docker, you need to use the docker run -p option to publish a port to the host, and then containers will be reachable via the published port via the host’s IP address or DNS name. In a Kubernetes context, you need to set up a Service that’s able to route traffic to the Pod (or Pods) that are running your container, and you ultimately reach containers via that Service.
The container-internal IP addresses are essentially useless in many contexts. (They cannot be reached from off-host at all; in some environments you can’t even reach them from outside of Docker on the same host.) There are other mechanisms you can use to reach containers (docker run -p from outside Docker, inter-container DNS from within Docker) and you never need to look up these IP addresses at all.
Your question places a heavy emphasis on ping(1). This is a very-low-level debugging tool that uses a network protocol called ICMP. If sending packets using ICMP is actually core to your workflow, you will have difficulty running it in Docker or Kubernetes. I suspect you aren’t actually. Don’t worry so much about being able to directly ping containers; use higher-level tools like curl(1) if you need to verify that a request is reaching its container.
It's pretty easy actually, assuming you have control over the routing tables of your external devices (either directly, or via your LAN's gateway/router). Assuming your containers are using a bridge network of 172.17.0.0/16, you add a static entry for the 172.17.0.0/16 network, with your Docker physical LAN IP as the gateway. You might need to also allow this forwarding in your Docker OS firewall configuration.
After that, you should be able to connect to your docker container using its bridge address (172.17.0.2 for example). Note however that it will likely not respond to pings, due to the container's firewall.
If you're content to access your container using only the bridge IP (and never again use your Docker host IP with the mapped-port), you can remove port mapping from the container entirely.
You need to create a new bridge docker network and attach the container to this network. You should be able to connect by this way.
docker network create -d bridge my-new-bridge-network
or
docker network create --driver=bridge --subnet=192.168.0.0/16 my-new-bridge-network
connect:
docker network connect my-new-bridge-network container1
or
docker network connect --ip 192.168.0.10/16 my-new-bridge-network container-name
If the problem persist, just reload docker daemon, restart the service. Is a known issue.
is it possible to change the ip of docker0 or provide a static IP to docker containers, because by default docker containers have the ip range of 172.17.0.2/16 but my network is 192.168.X.X/24 in this situation on the server container is running there all the containers is able to communicate within servers but from other server this failed to connect.
How do you set up your cluster? Do you use Swarm? If so, you need to use a k/v storage backend to enable communication between two containers hosted on different hosts. Is this what you aim to do, or do you want the host to communicate with the container on the other host?
Anyway, the solution is similar.
I re-writing a tuto for Docker Swarm to pull request it into their Swarm doc, you may want to take a look: https://www.auzias.net/en/docker-network-multihost/
Have a nice day!
problem can be fix by using --network=host
this will allow your container to use the host machine network. for direct accessing your container you can change the ssh port of the container and access your container with the specific port number.
I answered a similar question here
https://stackoverflow.com/a/35359185/4094678
The difference in your case would be to create a netowrk with subnet 192.168.X.X/24 and then assign desired ip addr to container with --ip
Here we can't able to change docker0 Ip address, but we have option to create multiple networks.
Solution 1:
can be by using start container with host network --network=host
Solution2:
we can also start the container by exposing the cluster required port and from another node we can communicate it.
-p hostport:serviceport
Or, Solution3:
We can deploy cluster over docker swarm.
I am having a weird scenario in my project.
I am running "Supervisor" application in one of docker container.
Using this supervisor I am running two "web applications" in docker containers and both are using one micro service; again installed in another docker container.
Now, I can able to access my application from "Supervisor's container". But obviously it is not accessible from my machine.
How can I able to access my applications "Web App1" or "Web App2" from my machine?
I have less knowledge related to docker networking.
Please help.
You can map ports of Web App1 and Web App2 to the host container and using the IP address and port you can access those containers from you machine. A better way to do this is to add hostname for your containers and maps ports so you don't have to remember the IP addresses since they are generated randomly on every time the container is recreated.
Docker manages network traffic between "host machine" and containers. In this case you have many dockers on different layers. On each layer you have to expose the ports of the internal containers to the "docker host" on the next layer and so on.
This is a solution over ports:
So the "Supervisor" on 172.17.42.1 must expose the ports of all the internal containers (172.17.0.2-4) as its own ports. So for "Supervisor" you need a -p docker parameter for each port of all containers inside the "Supervisor".
Expose the network:
Configure the local machine to send any network packet 172.17.*.* to 172.17.42.1. Then configure 172.17.42.1 to send network packages for IPs 172.17.0.* to its network adapter Docker0 (default docker network adapter). The exact implementation is dependent on your distribution.
Another solution:
Skip your Supervisor container and use docker-compose to arrange and manage your internal containers.