I have a basic question about Docker that is probably due to lack of knowledge on my part about networking. The Docker container networking documentation states:
By default, when you create a container, it does not publish any of its ports to the outside world. To make a port available to services outside of Docker, or to Docker containers which are not connected to the container’s network, use the --publish or -p flag. This creates a firewall rule which maps a container port to a port on the Docker host.
It sounds like, when you install a container on your computer without mapping any ports from the container to the host machine, the container should not be able to access the internet. However, for example, I install the Ubuntu container with:
docker pull ubuntu
Then I enter the container's command line with:
docker run -ti ubuntu bash
At that point, I can run apt-get update and the container starts pulling information from the internet without mapping any ports (e.g. -p 80:80). How is this possible?
Publishing a port allows machines external to the docker host to access the container, inbound connectivity. By default, containers can access the network with outbound connectivity.
To restrict a container from accessing the network, you can either run the container with no network (note: this still creates a loopback interface, and you can later connect it to another network):
docker run --net none ...
Or you can create a network with the --internal option and run containers on that network:
docker network create --internal internal
docker run --net internal ...
The internal network is created without a gateway interface on the bridge network.
When they talk about publishing ports, they mean inbound ports.
Outbound ports work - depending on your network type - see here for more:
https://docs.docker.com/network/
Related
I am trying to connect and run a device (LiDAR) through Docker container since it needs Ubuntu 16 while my computer is Ubunutu 20.
I got the device to ping inside the docker container, but it is not recognised when I try to use it.
What I did:
Made Dockerfile with requirements (Added EXPOSE to expose all ports)
Built docker image using:
docker build -t testLidar
I then made a container using
docker run -d -P --name test_Lidar (imagename)
Then
docker exec -t test_Lidar (device_ip) works
I am able to ping my LiDAR IP inside the container, but when I do ip a I cannot see the interfaces connected to my machine.
Been stuck on this for 3 days, any suggestions?
Note: I have done the exact same steps but on an Ubuntu 16 machine. The only change was the docker run command had --net host instead of -P tag and my device worked perfectly. I feel like this is the root of my problem.
Use --net host flag with docker run to attach the container to your host's networking stack and make it available in for other hosts in your network.
When you use --net host, you actually attach the container to your host's networking stack. By default, containers are attached to the default network of type bridge and can communicate with each other. You can then reach them only from your host using its ip addresses typically in subnet 172.17.0.0/16.
Using -P actually binds exposed ports from a container with randomly selected free ports on your host. It should be used for exposing network services (eg. web server with port 80), but not for ICMP ping.
I'm working with Docker containers for a while now but can't figure out how to ping docker containers which are part of my host network.
So until now I created my containers specifing the name and networks flags like described in many tutorials like: https://www.digitalocean.com/community/questions/how-to-ping-docker-container-from-another-container-by-name
Where I am able to create a network and afterwards run my containers in these networks for example like:
docker run -d --name web1 -n testnetwork
docker run -d --name web2 -n testnetwork
That would enable me to ping my containers from each other with:
docker exec -it web1 bash # enter container
ping web2 #ping second container
Now I have to use a given application which only runs in the "host" network for now. To access this container from my other containers they have to be in the same network (== "host").
But It seems like I cant ping my containers from each other anymore. I'm also unable to ping my containers from my host machine using their name.
Did I overlooked something?
Any help would be appreciated!
Best regards
If you set --network host, you basically disable Docker's entire networking stack. Among other things, that disables normal inter-container communications: if you're using host networking you can't call another container by its name. Host networking is very rarely necessary (and doesn't work well on some host platforms); the first thing I'd look at is whether you can switch back to standard (bridged) networking.
If you do run a container with --network host, it's indistinguishable from other processes running on that host. That means you can't directly send ICMP packets to it, any more than you can ping(1) your ssh daemon or Web browser. You need to connect to the container using the host's IP address or DNS name, even from other containers on the same host. From inside of a Docker container, how do I connect to the localhost of the machine? discusses several ways to do this.
(I don't think you can customize the behavior of Docker or Linux when a container receives an ICMP ECHO packet; ping(1) a container doesn't seem that useful.)
I'm trying to run multiple containers with the same ports on docker.
For this, I have created a network in brigde mode and specified a subnet.
docker network create -d --subnet 192.168.99.0/24 mynetwork
Then connected the docker containers to it with a static IP.
docker run -i -t -d -p 2377:2377 -p 7946:7946 -p 4789:4789-name container image
docker network connect --ip 192.168.99.98 mynetwork container
I did this with three containers (using different IP's), after starting the second one I got:
Error response from daemon: driver failed programming external connectivity on endpoint container(...): Bind for 0.0.0.0:7946 failed: port is already allocated
As far as I'm concerned, I should not be getting this error, due to bridge mode.
The docker run -p option allocates a port on the host system; those are shared across all containers, independently of what Docker-private network they’re using. These also will conflict with non-Docker processes running on the host.
If your goal is just to be able to communicate between containers on the same network, you don’t need a -p option at all. They can use each others’ --name and the port the service inside the container is listening on to connect.
If you’re trying to run multiple Docker container stacks at the same time, you need to decide which specific instance port 2377 on your host will route to, and change the other container’ -p option.
Specifically setting the Docker-internal private IP addresses (or worrying about them at all) is almost never necessary. I’d delete those --subnet and --ip options. To communicate between containers, put them on the same network as described above; from outside you need a (unique) -p option.
Can you give me one guide or graph to understand the difference?
The reason why I ask this question is I can't open website with the following method:
docker network create -d bridge mybridge
docker run -d --net mybridge --name db redis
docker run -d --net mybridge -e DB=db -p 8000:5000 --name web chrch/web
But I can open website with the following method:
docker run --rm -d --network host --name my_nginx nginx
I use google cloud platform VM instance and install docker by myself.
According to the docker documentation about bridge networking:
In terms of Docker, a bridge network uses a software bridge which allows containers connected to the same bridge network to communicate, while providing isolation from containers which are not connected to that bridge network.
According to the docker documentation about host networking
If you use the host network driver for a container, that container’s network stack is not isolated from the Docker host. For instance, if you run a container which binds to port 80 and you use host networking, the container’s application will be available on port 80 on the host’s IP address.
If you want to deploy multiple containers connected between them with a private internal network use bridge networking. If you want to deploy a container connected to the same network stack as the host (and access the same networks as the host) use host networking. If you simply want to publish some ports, run the container with the --publish or -p option, such as -p 8080:80.
In your first example I'd expect the application to be reachable on the host's IP address at port 8000 (the remapped port), and in the second port 5000 (there is no remapping option with host networking). If there's some sort of configuration or firewalling issue preventing this from working you should address that, rather than hack around it with --net host.
Bridge networking is Docker's standard networking mode. You should prefer it if at all possible. There are, confusingly, two different modes of it, but the form you show with an explicit docker network create is a best practice and you should use it if at all possible. Host networking completely disables Docker's network isolation. It means containers see and use exactly the same network interfaces the host has available, without an intermediate NAT layer.
With bridge networking, you need the docker run -p option to make specific ports visible outside of Docker. As an operator you can remap ports, bind to specific interfaces on a multi-homed system, or simply decline to make a service visible to other hosts at all. The explicit docker network create form lets containers connect to each other using their docker run --name as host names. If you're running multiple application stacks on the same host, they can be partially isolated from each other by using separate networks. Each container has its own separate network space, and localhost means "this container". This mode is also an easy step to the networking models in multi-host systems like Docker Swarm or Kubernetes.
With host networking, none of the above works at all; you cannot use docker run --net host -p ... and you have no choice about where or how ports are exposed. You can't reach other containers, unless they're configured to publish ports themselves. Since you're using the host's network, localhost means the host's view of itself.
For all that it's frequently recommended in SO answers, --net host is rarely necessary. The two cases I can think of off hand are for a service that needs to interrogate the host's network stack (for instance, a service-discovery system like Consul needs to know every port the host is listening on to advertise that) or for a service that has a large or inconsistent set of ports it uses. If you're using --net host because you've hard-coded localhost in your application, you're better off making that configurable..
Feature
Bridge
Host
Driver
The Bridge network is provided by the Bridge driver
The host network is provided by the host driver.
Default
bridge is the default network and provided by a bridge driver
Host does not default.
Connectivity
The bridge driver provides intercontainer connectivity for all containers running on the same machine.
The host driver instructs Docker not to create any special networking namespace or resources for attached containers.
How to access or connect to a process running on docker on host A from a remote host B
consider a Host A with ip 192.168.0.3 which is running a application on docker on port 3999 .
If i want to access that application from remote machine with IP 192.168.0.4 in same subnet.
To be precise i am running Kafka producer on the server and i am trying to receive using Kafka-console-Consumer.
Use --net=host to run your container and it'll use the host's network stack, then you can connect to the application running inside container like it's running on host directly.
Port mapping, use option -p to map the port inside your container to a port of your host. e.g. docker run -d -p <container port>:<host port> <image>, then you can connect to <host>:<host port> to connect your application inside container
Docker's built-in multi-host network. In early releases the network driver is isolated from docker's core, you have to use 3rd party tools like flannel or weave for multi-host connection, but from release 1.9, it has been merged into docker. You can follow it's guide to set it up.
Hope this is helpful :-)
First you need to bind docker container's port to the Host A:
docker run -d -p 3999:3999 kafka-producer
Then you need to access Host A from Host B using IP:Port
192.168.0.3:3999