Is --hostname like a domain name system in docker container environment that can replace --ip when referring to other container?
The --hostname flag only changes the hostname inside your container. This may be needed if your application expects a specific value for the hostname. It does not change DNS outside of docker, nor does it change the networking isolation, so it will not allow others to connect to the container with that name.
You can use the container name or the container's (short, 12 character) id to connect from container to container with docker's embedded dns as long as you have both containers on the same network and that network is not the default bridge.
--hostname is a parameter which can be given along with docker run command which will set the specified name as containers hostname whereas --ip is parameter to set specific ip address(ipv4) to that particular container.
docker run --hostname test --ip 10.1.2.3 ubuntu:14.04
The following command will create a docker container with base image as ubuntu-14.04 with hostname as test and container ip address as 10.1.2.3
If you need to change the hostname in a way that other containers from the same network will see it, just use --net-alias=${MY_NEW_DNS_NAME}
For example:
docker run -d --net-alias=${MY_NEW_DNS_NAME} --net=my-test-env --name=my-docker-name-test <dokcer-contanier>
Please see: Difference between --link and --alias in overlay docker network?
This is not a direct answer, I just want to summarise something that is not immediately clear.
To get containers to talk to each other,
Create a non default network:
docker network create MyNetwork
Connect containers to this network at run time:
docker run --network MyNetwork --name Container1 Image1
docker run --network MyNetwork --name Container2 Image2
Now, if Container1 is for example a web server running on port 80, Processes inside Container2 will be able to resolve it using a host name of Container1 and port 80
Further if Container1 is set up like this:
docker run --network MyNetwork --name Container1 -p 8080:80 Image1
Then
Container2 can access Container1:80
the Host can access 127.0.0.1:8080
This is summarised from here https://jaaq.medium.com/making-docker-containers-talk-to-each-other-by-hostname-using-container-networking-94835a6f6a5b
You can also confirm containers are connected and check their internal IP addresses using this:
docker network inspect MyNetwork
Related
I have 3 docker applications(containers) in which one container is communicating with other 2 containers. If I run that containers using below command, container 3 is able to access the container 1 and container 2.
docker run -d --network="host" --env-file container1.txt -p 8001:8080 img1:latest
docker run -d --network="host" --env-file container2.txt -p 8080:8080 img2:latest
docker run -d --network="host" --env-file container3.txt -p 8000:8080 img3:latest
But this is working only with host network if I remove this --network="host" option then I am not able to access this application outside(on web browser). In order to access it outside i need to make the host port and container ports same as below.
docker run -d --env-file container1.txt -p 8001:8001 img1:latest
docker run -d --env-file container2.txt -p 8080:8080 img2:latest
docker run -d --env-file container3.txt -p 8000:8000 img3:latest
With this above commands i am able to access my application on web browser but container 3 is not able to communicate with container 1. here container 3 can access the container 2 because there i am exposing 8080 host + container port. But i can't expose again 8080 host port for container 3.
How to resolve this issue??
At last my goal is this application should be accessible on browser without using host network, it should use the bridge network . And container 3 needs to communicate with container 1 & 2.
On user-defined networks, containers can not only communicate by IP address but can also resolve a container name to an IP address. This capability is called automatic service discovery.
Read this for more details on Docker container networking.
You can perform the following steps to achieve the desired result.
Create a private bridge network.
docker network create --driver bridge privet-net
Now start your application containers along with the --network private-net added to your docker run command.
docker run -d --env-file container1.txt -p 8001:8001 --network private-net img1:latest
docker run -d --env-file container2.txt -p 8080:8080 --network private-net img2:latest
docker run -d --env-file container3.txt -p 8000:8000 --network private-net img3:latest
With this way, all the three containers will be able to communicate with each other and also to the internet.
In this case when you are using --network=host, then you are telling docker to not isolate the network rather to use the host's network. So all the containers are on the same network, hence can communicate with each other without any issues. However when you remove --newtork=host, then docker will isolate the network as well there by restricting container 3 to communicate with container 1.
You will need some sort of orchestration service like docker compose, docker swarm etc.
I've got two Docker containers that need to have a websocket connection between the two.
I run one container like this:
docker run --name comm -p 8080:8080 comm_module:latest
to expose port 8080 to the host. Then I try to run the second container like this:
docker run --name test -p 8080:8080 datalogger:latest
However, I get the error below:
docker: Error response from daemon: driver failed programming external
connectivity on endpoint test
(f06588ee059e2c4be981e3676d7e05b374b42a8491f9f45be27da55248189556):
Bind for 0.0.0.0:8080 failed: port is already allocated. ERRO[0000]
error waiting for container: context canceled
I'm not sure what to do. Should I connect these to a network? How do I run these containers?
you can't bind the same host port twice in the same time you may change one of the ports on one container:
docker run --name comm -p 8080:8080 comm_module:latest
docker run --name test -p 8081:8080 datalogger:latest
you may check the configuration in the containers on how they communicate .
you can also create link between them:
docker run --name test -p 8081:8080 --link comm datalogger:latest
I finally worked it out. These are the steps involved for a two-way websocket communication between two Docker containers:
Modify the source code in the containers to use the name of the other container as the destination host address + port number (e.g. comm:port_no inside test, and vice versa).
Expose the same port (8080) in the Dockerfiles of the two containers and build the images. No need to publish them as they are will be visible to other containers on the network.
Create a user-defined bridge network like this:
docker network create my-net
Create my first container and attach it to the network:
docker create --name comm --network my-net comm_module:latest
Create my second container and attach it to the network:
docker create --name test --network my-net datalogger:latest
Start both containers by issuing the docker start command.
And the two-way websocket communication works nicely!
My Solution works fine.
docker network create mynet
docker run -p 443:443 --net=mynet --ip=172.18.0.3 --hostname=frontend.foobar.com foobarfrontend
docker run -p 9999:9999 --net=mynet --ip=172.18.0.2 --hostname=backend.foobar.com foobarbackend
route /P add 172.18.0.0 MASK 255.255.0.0 10.0.75.2
the foobarfrontend calls a wss websocket on foobarbackend on port 9999
PS: i work on docker windows 10 with linuxcontainers
have fun
I am running Docker for Mac. When I run
docker run -d --rm --name nginx -p 80:80 nginx:1.10.3
I can access Nginx on port 80 on my Mac. When I run
docker run -d --rm --name nginx --network host -p 80:80 nginx:1.10.3
I can not.
Is it possible to use both "--network host" and publish a port so that it is reachable from my Mac?
Alternatively, can I access Nginx from my Mac via the IP of the HyperKit VM?
Without the --network flag the container is added to the bridge network by default; which creates a network stack on the Docker bridge (usually the veth interface).
If you specify --network host the container gets added to the Docker host network stack. Note the container will share the networking namespace of the host, and thus all its security implications.
Which means you don't need to add -p 80:80, instead run...
docker run -d --rm --name nginx --network host nginx:1.10.3
and access the container on http://127.0.0.1
The following link will help answer the HyperKit question and the current limitations:
https://docs.docker.com/docker-for-mac/networking/
There is no docker0 bridge on macOS
Because of the way networking is implemented in Docker for Mac, you
cannot see a docker0 interface in macOS. This interface is actually
within HyperKit.
I have a container1 running a service1 on port1
also
I have a container2 running a service2 on port2
How can I access service2:port2 from service1:port1?
I mention that the container are linked together.
I ask if there is a way to do it without accessing the docker0 IP (where the port is visible)
thanks
The preferred solution is to place both containers on the same network, use the build-in dns discovery to reach the other node by name, and you'll be able to access them by the container port, not the host published port. By CLI, that looks like:
docker network create testnet
docker run -d --net testnet --name web nginx
docker run -it --rm --net testnet busybox wget -qO - http://web
The busybox shows a sample client container connecting to the nginx container with the name web, over port 80. Note that this port didn't need to be published to be reachable by other containers.
Setting up multi-container environments with their own network is a common task for docker-compose, so I'd recommend looking into this tool if you find yourself doing this a lot.
I'm following the following tutorial on how to start a basic nginx server in a docker container. However, the example's nginx docker container runs on localhost (0.0.0.0) as shown here:
Meanwhile, when I run it it for some reason it runs on the IP 10.0.75.2:
Is there any particular reason why this is happening? And is there any way to get it to run on localhost like in the example?
Edit: I tried using --net=host but had no results:
The default network is bridged. The 0.0.0.0:49166->443 shows a port mapping of exposed ports in the container to high level ports on your host because of the -P option. You can manually map specific ports by changing that flag to something like -p 8080:80 -p 443:443 to have port 8080 and 443 on your host map into the container.
You can also change the default network to be your host network as you've requested. This removes some of the isolation and protections provided by the container, and limits your ability to configure integrations between containers, which is why it is not the default option. That syntax would be:
docker run --name nginx1 --net=host -d nginx
Edit: from your comments and a reread I see you're also asking about where the 10.0.75.2 ip address comes from. This is based on how you launch the docker daemon. That IP binding is assigned when you pass the --ip flag to the daemon documentation here. If you're running docker in a vm with docker-machine, I'd expect this to be the IP of your vm.
A good turnaround is to set using -p flag (--publish short)
docker run -d -p 3000:80 --name <your_image_name> nginx:<version_tag>