I want to map container port only to internal docker bridge (172.17.0.*)
If it's possible ?
Thanks for help
All ports between containers on the same docker network are accessible to each other. There is no need to expose ports, expose is only needed to document the port by the image creator for the admin running the container. Publishing ports is only needed to make a specific port available outside of the host. For your requirement, there's nothing to do, it's the default behavior.
Related
What is the difference between ports and expose options in docker-compose.yml?
According to the docker-compose reference,
Ports is defined as:
Expose ports. Either specify both ports (HOST:CONTAINER), or just the container port (a random host port will be chosen).
Ports mentioned in docker-compose.yml will be shared among different services started by the docker-compose.
Ports will be exposed to the host machine to a random port or a given port.
My docker-compose.yml looks like:
mysql:
image: mysql:5.7
ports:
- "3306"
If I do docker-compose ps, it will look like:
Name Command State Ports
-------------------------------------------------------------------------------------
mysql_1 docker-entrypoint.sh mysqld Up 0.0.0.0:32769->3306/tcp
Expose is defined as:
Expose ports without publishing them to the host machine - they’ll only be accessible to linked services. Only the internal port can be specified.
Ports are not exposed to host machines, only exposed to other services.
mysql:
image: mysql:5.7
expose:
- "3306"
If I do docker-compose ps, it will look like:
Name Command State Ports
---------------------------------------------------------------
mysql_1 docker-entrypoint.sh mysqld Up 3306/tcp
Edit
In recent versions of Dockerfile, EXPOSE doesn't have any operational impact anymore, it is just informative. (see also)
ports:
Activates the container to listen for specified port(s) from the world outside of the docker(can be same host machine or a different machine) AND also accessible world inside docker.
More than one port can be specified (that's is why ports not port)
expose:
Activates container to listen for a specific port only from the world inside of docker AND not accessible world outside of the docker.
More than one port can be specified
Ports
This section is used to define the mapping between the host server and Docker container.
ports:
- 10005:80
It means the application running inside the container is exposed at port 80. But external system/entity cannot access it, so it need to be mapped to host server port.
Note: you have to open the host port 10005 and modify firewall rules to allow external entities to access the application.
They can use
http://{host IP}:10005
something like this
EXPOSE
This is exclusively used to define the port on which application is running inside the docker container.
You can define it in dockerfile as well. Generally, it is good and widely used practice to define EXPOSE inside dockerfile because very rarely anyone run them on other port than default 80 port
Ports
The ports section will publish ports on the host. Docker will set up a forward for a specific port from the host network into the container. By default, this is implemented with a userspace proxy process (docker-proxy) that listens on the first port, and forwards into the container, which needs to listen on the second point. If the container is not listening on the destination port, you will still see something listening on the host, but get a connection refused if you try to connect to that host port, from the failed forward into your container.
Note, the container must be listening on all network interfaces since this proxy is not running within the container's network namespace and cannot reach 127.0.0.1 inside the container. The IPv4 method for that is to configure your application to listen on 0.0.0.0.
Also note that published ports do not work in the opposite direction. You cannot connect to a service on the host from the container by publishing a port. Instead you'll find docker errors trying to listen to the already-in-use host port.
Expose
Expose is documentation. It sets metadata on the image, and when running, on the container too. Typically, you configure this in the Dockerfile with the EXPOSE instruction, and it serves as documentation for the users running your image, for them to know on which ports by default your application will be listening. When configured with a compose file, this metadata is only set on the container. You can see the exposed ports when you run a docker inspect on the image or container.
There are a few tools that rely on exposed ports. In docker, the -P flag will publish all exposed ports onto ephemeral ports on the host. There are also various reverse proxies that will default to using an exposed port when sending traffic to your application if you do not explicitly set the container port.
Other than those external tools, expose has no impact at all on the networking between containers. You only need a common docker network, and connecting to the container port, to access one container from another. If that network is user created (e.g. not the default bridge network named bridge), you can use DNS to connect to the other containers.
I totally agree with the answers before.
I just like to mention that the difference between expose and ports is part of the security concept in docker. It goes hand in hand with the networking of docker.
For example:
Imagine an application with a web front-end and a database back-end.
The outside world needs access to the web front-end (perhaps on port
80), but only the back-end itself needs access to the database host
and port. Using a user-defined bridge, only the web port needs to be
opened, and the database application doesn’t need any ports open,
since the web front-end can reach it over the user-defined bridge.
This is a common use case when setting up a network architecture in docker.
So for example in a default bridge network, not ports are accessible from the outer world.
Therefor you can open an ingresspoint with "ports". With using "expose" you define communication within the network. If you want to expose the default ports you don't need to define "expose" in your docker-compose file.
As we expose the container port in dockerfile itself then what is the use of container port in kubernetes yaml. What does it actually do. Is it mandatory to mention the container port in yaml file or we need not to mention in when we expose it in docker file.
Anyways, we will be using target port the map the container port with pod
ports:
- containerPort: 80
ports :
containerPortList of ports to expose from the container. Exposing a
port here gives the system additional information about the network
connections a container uses, but is primarily informational. Not
specifying a port here DOES NOT prevent that port from being exposed.
Any port which is listening on the default "0.0.0.0" address inside
a container will be accessible from the network. Cannot be
updated.
container-core
So it is exactly same with docker EXPOSE instruction. Both are informational. If you don’t configure ports in Kubernetes deployment, you can still access to the ports using Pod IP inside the cluster. You can create a service to access the ports externally without configuring ports in the deployment. But it is good to configure. It will help you or others to understand the deployment configuration better.
The EXPOSE instruction does not actually publish the port. It
functions as a type of documentation between the person who builds the
image and the person who runs the container, about which ports are
intended to be published.
.docker-reference-builder
If we have two applications app1.py and app2.py both running in docker container as flask services with following commands:
docker run -p 5000:5002 app1.py
docker run -p 9000:5002 app2.py
Is it possible to keep the same docker port 5002 for both containers?
Secondly, if I use app.run(host='0.0.0.0', port=5000, debug=True) in flask endpoint.py file which is used for image building, is port=5000 the docker port in container or the port available externally on host?
Yes, each container runs in an isolated network namespace, so every one can listen on the same port and they won’t conflict. Inside your application code the port you listen on is the container-internal port, and unless you get told in some other way (like an HTTP Host: header) you have no way of knowing what ports you’ve been remapped to externally.
Is it possible to keep the same docker port 5002 for both containers?
Yes, of course. Typically every container runs in an isolate network namespace, which means containers cannot communicate with each unless they are configured to do so. What confuses you maybe that containers do communicate with each other well by default, which should thank Docker network default setting. But there are still other use cases. You may see more about The container Network Model and network namespace here.
Is port=5000 the port in container or the port valid externally on host?
It’s the port in container with no doubt. We could notice it is a user-defined argument for function run() in Flask. Since Flask application runs in container, so 5000 will be the port which Flask app would listen on in container.
We should map it out if we wanna access 5000 on host(outside of container). The flag -p would help you.
Hope this helps~
What is the difference between ports and expose options in docker-compose.yml?
According to the docker-compose reference,
Ports is defined as:
Expose ports. Either specify both ports (HOST:CONTAINER), or just the container port (a random host port will be chosen).
Ports mentioned in docker-compose.yml will be shared among different services started by the docker-compose.
Ports will be exposed to the host machine to a random port or a given port.
My docker-compose.yml looks like:
mysql:
image: mysql:5.7
ports:
- "3306"
If I do docker-compose ps, it will look like:
Name Command State Ports
-------------------------------------------------------------------------------------
mysql_1 docker-entrypoint.sh mysqld Up 0.0.0.0:32769->3306/tcp
Expose is defined as:
Expose ports without publishing them to the host machine - they’ll only be accessible to linked services. Only the internal port can be specified.
Ports are not exposed to host machines, only exposed to other services.
mysql:
image: mysql:5.7
expose:
- "3306"
If I do docker-compose ps, it will look like:
Name Command State Ports
---------------------------------------------------------------
mysql_1 docker-entrypoint.sh mysqld Up 3306/tcp
Edit
In recent versions of Dockerfile, EXPOSE doesn't have any operational impact anymore, it is just informative. (see also)
ports:
Activates the container to listen for specified port(s) from the world outside of the docker(can be same host machine or a different machine) AND also accessible world inside docker.
More than one port can be specified (that's is why ports not port)
expose:
Activates container to listen for a specific port only from the world inside of docker AND not accessible world outside of the docker.
More than one port can be specified
Ports
This section is used to define the mapping between the host server and Docker container.
ports:
- 10005:80
It means the application running inside the container is exposed at port 80. But external system/entity cannot access it, so it need to be mapped to host server port.
Note: you have to open the host port 10005 and modify firewall rules to allow external entities to access the application.
They can use
http://{host IP}:10005
something like this
EXPOSE
This is exclusively used to define the port on which application is running inside the docker container.
You can define it in dockerfile as well. Generally, it is good and widely used practice to define EXPOSE inside dockerfile because very rarely anyone run them on other port than default 80 port
Ports
The ports section will publish ports on the host. Docker will set up a forward for a specific port from the host network into the container. By default, this is implemented with a userspace proxy process (docker-proxy) that listens on the first port, and forwards into the container, which needs to listen on the second point. If the container is not listening on the destination port, you will still see something listening on the host, but get a connection refused if you try to connect to that host port, from the failed forward into your container.
Note, the container must be listening on all network interfaces since this proxy is not running within the container's network namespace and cannot reach 127.0.0.1 inside the container. The IPv4 method for that is to configure your application to listen on 0.0.0.0.
Also note that published ports do not work in the opposite direction. You cannot connect to a service on the host from the container by publishing a port. Instead you'll find docker errors trying to listen to the already-in-use host port.
Expose
Expose is documentation. It sets metadata on the image, and when running, on the container too. Typically, you configure this in the Dockerfile with the EXPOSE instruction, and it serves as documentation for the users running your image, for them to know on which ports by default your application will be listening. When configured with a compose file, this metadata is only set on the container. You can see the exposed ports when you run a docker inspect on the image or container.
There are a few tools that rely on exposed ports. In docker, the -P flag will publish all exposed ports onto ephemeral ports on the host. There are also various reverse proxies that will default to using an exposed port when sending traffic to your application if you do not explicitly set the container port.
Other than those external tools, expose has no impact at all on the networking between containers. You only need a common docker network, and connecting to the container port, to access one container from another. If that network is user created (e.g. not the default bridge network named bridge), you can use DNS to connect to the other containers.
I totally agree with the answers before.
I just like to mention that the difference between expose and ports is part of the security concept in docker. It goes hand in hand with the networking of docker.
For example:
Imagine an application with a web front-end and a database back-end.
The outside world needs access to the web front-end (perhaps on port
80), but only the back-end itself needs access to the database host
and port. Using a user-defined bridge, only the web port needs to be
opened, and the database application doesn’t need any ports open,
since the web front-end can reach it over the user-defined bridge.
This is a common use case when setting up a network architecture in docker.
So for example in a default bridge network, not ports are accessible from the outer world.
Therefor you can open an ingresspoint with "ports". With using "expose" you define communication within the network. If you want to expose the default ports you don't need to define "expose" in your docker-compose file.
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.