This might be a very simple question but I haven't been able to find anything about it online.
When running docker images, either through docker start or docker compose, what is the hostname that is assigned to it if hostname is not defined?
Does it grab the container name and set it as the hostname?
Related
I am trying to make a shared folder from a container with Ubuntu installing samba.
It is a test and I want to do it without creating volumes.
So, how could I see the IP of the container to create the folder in Windows?
I've been doing it with docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' containerId but the IP that it returns are only for internal networks to docker
Run the container by mapping a host port and you should be able to access the container instance with HostIP:HostPort
RUN A FTP server in the container and Expose necessary ports, including SSH PORT.
Try accessing the files over FTP
Have you tried the following command?
docker container ps
Check out the ports attribute, this should give you the output you need.
In case of I have a machine that running docker (docker host) and spin up some containers inside this docker host,
I need containers' services be able to talk to each other - container expose ports and they also need to resolve by hostname (e.g: example.com)
container A needs to talk to container B with URL: example.com:3000
I've read this article but not quite sure about "inherit" from docker host, does docker host's /etc/hosts will be appended to container's /etc/hosts that running inside docker host?
https://docs.docker.com/engine/reference/run/#managing-etchosts
How to achieve?
Does this "inherit" has any connect to type of docker container networking https://docs.docker.com/v17.09/engine/userguide/networking/ ?
It does not inherit the host's /etc/hosts file. The file inside your container is updated by docker when using the --add-host parameter or extra_hosts in docker-compose. You can add individual records by using extra_hosts in docker-compose (https://docs.docker.com/compose/compose-file/#extra_hosts).
Although if you're just trying to get 2 containers talking to each other you can alternatively connect them to the same network. In docker-compose you can create what's called an external network and have all your docker-compose files reference it. you will then be able to connect by using the full docker container name (eg. http://project_app_1:3000).
See https://docs.docker.com/compose/compose-file/#external
WIthin a Docker container, I would like to connect to a MySQL database that resides on the local network. However, I get errors because it can not find the host name, so my current hot fix is to hardcode the IP (which is bound to change at some time).
Hence; is it possible to forward a hostname from the host machine to the Docker container at docker run?
Yes, it is possible. Just inject hostname variable when run docker run command:
$ hostname
np-laptop
$ docker run -ti -e HOSTNAME=$(hostname) alpine:3.7
/ # env
HOSTNAME=np-laptop
SHLVL=1
HOME=/root
TERM=xterm
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/
Update:
I think you can do two things with docker run for your particular case:
1. Bind /etc/hosts file from the host to a container.
2. Define any dns server you want inside a container with --dns flag.
So, finally the command is:
docker run -ti -v /etc/hosts:/etc/hosts --dns=<IP_of_DNS> alpine:3.7
Docker containers by default has access to the host network, and they're able to resolve DNS names using DNS servers configured on the host, so it should work out of the box.
I remember having similar problem in my corporate network, I solved it by referencing in the app the remote server with FQDN - our-database.mycompany.com instad just using our-database.
Hope this helps.
People has asked similar questions and got good answers:
How do I pass environment variables to Docker containers?
Alternatively you can configure the DHCP/DNS server that serves the docker machines to resolve the hostnames properly. DDNS is another option that can simplify configuration as well.
how is it possible to resolve names defined in Docker host's /etc/hosts in containers?
Containers running in my Docker host can resolve public names (e.g. www.ibm.com) so Docker dns is working fine.
I would like to resolve names from Docker hosts's (e.g. 127.17.0.1 smtp) from containers.
My final goal is to connect to services running in Docker host (e.g. smtp server) from containers. I know I can use the Docker Host IP (127.17.0.1) from containers, but I thought that Docker would have used the Docker host /etc/hosts to build containers's resolve files as well.
I am even quite sure I have seen this working a while ago... but I could be wrong.
Any thoughts?
Giovanni
Check out the --add-host flag for the docker command: https://docs.docker.com/engine/reference/run/#managing-etchosts
$ docker run --add-host="smtp:127.17.0.1" container command
In Docker, /etc/hosts cannot be overwritten or modified at runtime (security feature). You need to use Docker's API, in this case --add-host to modify the file.
For docker-compose, use the extra_hosts option.
For the whole "connect to services running in host" problem, see the discussion in this GitHub issue: https://github.com/docker/docker/issues/1143.
The common approach for this problem is to use --add-host with Docker's gateway address for the host, e.g. --add-host="dockerhost:172.17.42.1". Check the issue above for some scripts that find the correct IP and start your containers.
You can setup on host simple DNS server, and in container setup /etc/resolve.conf to Docker host DNS server.
For example in dnsmasq you can add addn-hosts=/etc/hosts to config file. So container, by using Docker host DNS server, will be able to resolve hosts /etc/hosts.
I want to run a task in some docker containers on different hosts. And I have written a manager app to manage the containers(start task, stop task, get status, etc...) . Once a container is started, it will send an http request to the manager with its address and port, so the manager will know how to manage the container.
Since there may be more than one containers running on a same host, they would be mapped to different ports. To register a container on my manager, I have to know which port each container is mapped to.
How can I get the mapped port inside a docker container?
There's an solution here How do I know mapped port of host from docker container? . But it's not applicable if I run container with -P. Since this question is asked more than 1 year ago, I'm wondering maybe there's a new feature added to docker to solve this problem.
You can also you docker port container_id
The doc
https://docs.docker.com/engine/reference/commandline/port/
examples from the doc
$ docker port test
7890/tcp -> 0.0.0.0:4321
9876/tcp -> 0.0.0.0:1234
$ docker port test 7890/tcp
0.0.0.0:4321
$ docker port test 7890/udp
2014/06/24 11:53:36 Error: No public port '7890/udp' published for test
$ docker port test 7890
0.0.0.0:4321
i share /var/run/docker.sock to container and get self info
docker run --rm -it -v /var/run/docker.sock:/var/run/docker.sock alpine:latest sh
in container shell
env //get HOSTNAME
curl --unix-socket /var/run/docker.sock http://localhost/containers/3c6b9e44a622/json
the 3c6b9e44a622 is your HOSTNAME
Once a container is started, it will send an http request to the manager with its address and port
This isn't going to be working. From inside a container you cannot figure out to which docker host port a container port is mapped to.
What I can think about which would work and be the closest to what you describe is making the container open a websocket connection to the manager. Such a connection would allow two ways communication between your manager and container while still being over HTTP.
What you are trying to achieve is called service discovery. There are already tools for service discovery that work with Docker. You should pick one of them instead of trying to make your own.
See for instance:
etcd
consul
zookeeper
If you really want to implement your service discovery system, one way to go is to have your manager use the docker event command (or one of the docker client librairies). This would enable your manager to get notified of containers creations/deletions with nothing to do on the container side.
Then query the docker host to figure out the ports that are mapped to your containers with docker port.