How does Docker decide whether a service persists? [duplicate] - docker

This question already has answers here:
Docker container will automatically stop after "docker run -d"
(22 answers)
Closed 10 days ago.
Given this simple Docker compose.yaml file:
services:
test:
image: node:18
website:
image: nginx
After running:
docker compose up
docker ps
I expected to see two running containers/images. Instead I got just the one:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c970ef47fb93 nginx "/docker-entrypoint.…" 51 seconds ago Up 48 seconds 80/tcp myid-website-1
What is happening here? Does Docker expect that a persistent process is kept running within the container image? How does it decide which services persist?
I also noticed that adding restart: always caused the Node image to perpetually restart. What would be a good way to get the Node image to start via Docker Compose, such that I could log into it via docker exec?
My instinct is that this has to do with the distinction between services and images/containers.

For a container to persist, it needs to run a program. When the program ends, the container is stopped.
The Nginx image runs the command nginx -g daemon off; which starts Nginx and then waits for requests to come in. It doesn't end.
The Node image runs the command node. When there's no arguments passed to it, it runs in interactive mode. But when you run it like you do, there's no TTY attached to the container, so node sees that there's no way to get any input. So node exits and the container is stopped.
If you run the command docker ps -a, you'll also see stopped containers. You'll then see that your node container has exited.

Related

Docker container keeps stopping after 'docker start'

I'm fairly new to Docker. I have a long Dockerfile that I inherited from a previous developer, which has many errors and I'm trying to get it back to a working point. I commented out most of the file except for just the first line:
FROM ubuntu:14.04
I did the following:
docker build -t pm . to build the image - this works because I can see the image when I execute docker images
docker run <image-id> returns without error or any message. Now I'm expecting the container to be created from the image and started. But when I do a docker ps -a it shows the container exited:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b05f9727f516 f216cfb59484 "/bin/bash" About a
minute ago Exited (0) About a minute ago
lucid_shirley
Not sure why can't I get a running container and why does it keep stopping after the docker run command.
executing docker logs <container_id> displays nothing - it just returns without any output.
Your Docker image doesn’t actually do anything, container stop when finish its job. Since here no foreground process running it will start and then immediately stop.
To confirm your container have no issues, try to put below code into a docker-compose.yml(in same folder as the Dockerfile) and run docker-compose up, now you will see your container is running without exiting.
version: '3'
services:
my-service:
build: .
tty: true
Please have a look here Docker official tutorial it will guide you to how to work with docker.
try
docker run -it <image> /bin/bash
to run a shell inside the container.
That won't do much for you, but that'll show you what is happening: as soon as you exit the shell, it will exit the container too.
Your container basically doesn't do anything: it has an image of Ubuntu but doesn't have an ENTRYPOINT or a CMD command to run 'something'
Containers are ephemeral when ran: they run a single command and exit when the command finishes.
Docker container categorized following way.
Task Based : When container start it will start processing and it complete the process then exited.
Background container : It will wait for some request.
As you not provided your docker file so I assume that you have only one statement.
FROM ubuntu:14.04
your build statement create image with name pm.
Now you run
docker run pm
It will start container and stop as you did not provide any entry point.
Now try this
This is one command prompt or terminal.
docker run -it pm /bin/bash
Open another terminal or command prompt.
docker ps ( Now you will see there is one container).
If you want to see container that is continuously running then use following image.
(This is just a example)
docker run -d -p 8099:80 nginx
Above line run one container with Nginx image and when you open your browser http://localhost:8099 you can see the response.
Docker Containers are closely related to the process they are running. This process is specified by the "CMD" part on the Dockerfile. This process has the PID "1". If you kill it, your container is killed. If you haven't one, your container will stop instantly. In your case, you have to "override" your CMD. You can do it with a simple : "docker run -it ubuntu:18.04 bash". "-it" is mandatory since it allows the stdin to be attached to your container.
Have fun with docker.
Each instruction of Dockerfile is a layer within a container which perform some task. In your docker file It's just the loading the ubuntu which is completed when you run the docker within a fraction of seconds and exit since process finished. So if want to have your container running all the time then there should be a foreground process running in your docker.
For testing if you run
docker run <imageid> echo hi it will return the output means your container is fine.

How to kill container generated by docker-compose?

(sorry using the term "kill" with quotes is not about docker-compose kill, is about "UNIX ps kill" after what the process really go out of the "UNIX ps list")
Usual docker run can be "killed" by usual docker stop, because after stop I not see the container at docker ps -a... If it is correct, there are a semantic bug with docker-compose because I can't "kill" the containers, they stay at docker ps.
After my simple docker-compose up (without &) I do ^C and the containers stay there at docker ps -a... Impossible to kill by docker compose stop.
NOTE: when I use ordinary docker run and after it docker stop there are nothing at docker ps -a, so I can say "I killed it".
Usual docker run can be "killed" by usual docker stop, because after stop I not see the container at docker ps.
No. docker stop just stops a running container, it doesn' t remove the container. This happens only in case you've used docker run --rm .... This --rm option means that when the container is stopped, it will be removed/deleted.
Docker
docker run ... creates and runs a container
docker stop ... stops a running container
docker start ... starts a stopped container
docker rm ... removes a stopped container
Docker Compose
docker-compose up creates and runs a collection of containers
docker-compose stop stops the containers
docker-compose start starts the containers
docker-compose down stops and removes the containers
Be careful...
As it discussed in the comments section, by using docker-compose down other things can also take place regarding volumes, networks. Keep in mind that you might lose data (if your container is a database for example) and make sure you have saved them or you are somehow able to create them again.
Check out running containers:
docker ps
Example output:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
e86521d81a96 app_php "docker-php-entrypoi…" 2 hours ago Up About an hour 0.0.0.0:8080->80/tcp app_php_1
7a30681b6255 mysql:5.6 "docker-entrypoint.s…" 3 hours ago Up About an hour 0.0.0.0:3306->3306/tcp app_db_1
21aa3eef5f42 phpmyadmin/phpmyadmin "/run.sh supervisord…" 4 hours ago Up About an hour 9000/tcp, 0.0.0.0:8081->80/tcp app_phpmyadmin_1
9afc52b3f82f mailhog/mailhog "MailHog" 4 hours ago Up About an hour 1025/tcp, 0.0.0.0:8082->8025/tcp app_mailhog_1
then stop one by the container id:
docker kill part_of_the_id/name
For instance:
docker kill e86 or docker kill app_php_1
Docker-compose is just a script to help you manage one or multiple containers running in a group and is absolutely not required to manage your containers.
To remove the container completely you have to remove the container docker rm container_id_or_name
To stop all running containers:
docker stop $(docker ps -q)
You can use docker rm <container-name> to do that. This command will stop and remove service container. Anonymous volumes attached to the container will not be removed.

moving docker-compose images between hosts

based on Moving docker-compose containersets
I have loaded the images :
$ docker images -a
REPOSITORY TAG IMAGE ID CREATED SIZE
br/irc latest 3203cf074c6b 23 hours ago 377MB
openjdk 8u131-jdk-alpine a2a00e606b82 5 days ago 101MB
nginx 1.13.3-alpine ba60b24dbad5 4 months ago 15.5MB
but now i want to run them, as they would run with docker-compose, but i cannot find any example.
here is the docker-compose.yml
version: '3'
services:
irc:
build: irc
hostname: irc
image: br/irc:latest
command: |
-Djava.net.preferIPv4Stack=true
-Djava.net.preferIPv4Addresses
run-app
volumes:
- ./br/assets/br.properties:/opt/br/src/java/br.properties
nginx:
hostname: nginx
image: nginx:1.13.3-alpine
ports:
- "80:80"
links:
- irc:irc
volumes:
- ./nginx/assets/default.conf:/etc/nginx/conf.d/default.conf
so how can i run the container, and attach to it, to see if its running, and in what order do i run these three images. Just started with docker, so not sure of the typical workflow ( build, run, attach etc )
so even though i do have docker-compose yml file, but since i have the build images from another host, can i possibly run docker commands to run and execute the images ? making sure that the local images are being referenced, and not the ones from docker registry.
Thanks #tgogos, this does give me a general overview, but specifically i was looking for:
$ docker run -dit openjdk:8u131-jdk-alpine
then:
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
cc6ceb8a82f8 openjdk:8u131-jdk-alpine "/bin/sh" 52 seconds ago Up 51 seconds vibrant_hodgkin
shows its running
2nd:
$ docker run -dit nginx:1.13.3-alpine
3437cf295f1c7f1c27bc27e46fd46f5649eda460fc839d2d6a2a1367f190cedc
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3437cf295f1c nginx:1.13.3-alpine "nginx -g 'daemon ..." 20 seconds ago Up 19 seconds 80/tcp vigilant_kare
cc6ceb8a82f8 openjdk:8u131-jdk-alpine "/bin/sh" 2 minutes ago Up 2 minutes vibrant_hodgkin
then: finally:
[ec2-user#ip-10-193-206-13 DOCKERLOCAL]$ docker run -dit br/irc
9f72d331beb8dc8ccccee3ff56156202eb548d0fb70c5b5b28629ccee6332bb0
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
9f72d331beb8 br/irc "/opt/irc/grailsw" 8 seconds ago Up 7 seconds 8080/tcp cocky_fermi
3437cf295f1c nginx:1.13.3-alpine "nginx -g 'daemon ..." 56 seconds ago Up 55 seconds 80/tcp vigilant_kare
cc6ceb8a82f8 openjdk:8u131-jdk-alpine "/bin/sh" 2 minutes ago Up 2 minutes vibrant_hodgkin
All three UP !!!!
Your question is about docker-compose but you also ask things about run, build, attach which makes me think I should try to help you with some basic information (which wasn't so easy for me to cope with a couple of months ago :-)
images
Images are somehow the base from which containers are created. Docker pulls images from http://hub.docker.com and stores them in your host to be used every time you create a new container. Changes in the container do not affect the base image.
To pull images from docker hub, use docker pull .... To build your own images start reading about Dockerfiles. A simple Dockerfile (in an abstract way) would look like this:
FROM ubuntu # base image
ADD my_super_web_app_files # adds files for your app
CMD run_my_app.sh # starts serving requests
To create the above image to your host, you use docker build ... and this is a very good way to build your images, because you know the steps taken to be created.
If this procedure takes long, you might consider later to store the image in a docker registry like http://hub.docker.com, so that you can pull it from any other machine easily. I had to do this, when dealing with ffmpeg on a Raspberry Pi (the compilation took hours, I needed to pull the already created image, not build it from scratch again in every Raspberry).
containers
Containers are based on images, you can have many different containers from the same image on the same host. docker run [image] creates a new container based on that image and starts it. Many people here start thinking containers are like mini-VMs. They are not!
Consider a container as a process. Every container has a CMD and when started, executes it. If this command finishes, or fails, the container stops, exits. A good example for this is nginx: go check the official Dockerfile, the command is:
CMD ["nginx"]
If you want to see the logs from the CMD, you can docker attach ... to your container. You can also docker stop ... a running container or docker start ... an already stopped one. You can "get inside" to type commands by:
docker exec -it [container_name] /bin/bash
This opens a new tty for you to type commands, while the CMD continues to run.
To read more about the above topics (I've only scratched the surface) I suggest you also read:
Is it possible to start a shell session in a running container (without ssh)
Docker - Enter Running Container with new TTY
How do you attach and detach from Docker's process?
Why docker container exits immediately
~jpetazzo: If you run SSHD in your Docker containers, you're doing it wrong!
docker-compose
After you feel comfortable with these, docker-compose will be your handy tool which will help you manipulate many containers with single line commands. For example:
docker compose up
Builds, (re)creates, starts, and attaches to containers for a service.
Unless they are already running, this command also starts any linked services.
The docker-compose up command aggregates the output of each container (essentially running docker-compose logs -f). When the command exits, all containers are stopped. Running docker-compose up -d starts the containers in the background and leaves them running
To run your docker-compose file you would have to execute:
docker-compose up -d
Then to see if your containers are running you would have to run:
docker ps
This command will display all the running containers
Then you could run the exec command which will allow you to enter inside a running container:
docker-compose exec irc
More about docker-compose up here: https://docs.docker.com/compose/reference/up/

Start an existing docker ubuntu container [duplicate]

This question already has answers here:
How to continue a Docker container which has exited
(14 answers)
Closed 6 years ago.
A related question & answer on How to start a docker container (ubuntu image) suggest using docker run -it ubuntu to start a ubuntu container and connect to it. However the run command creates and starts a new ubuntu container.
How do we start an existing docker container (ubuntu image) given it's CONTAINER_ID without creating a new container?
Example:
docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
9f297d02f419 ubuntu "/bin/bash" 3 seconds ago Exited (0) 1 seconds ago cranky_wilson
How do we start 9f297d02f419 ?
you can start the stopped container using docker start command -
eg:
docker start 9f297d02f419
If you just use run on the Ubuntu image it will start a container that's running no command, which will immediately stop. You can docker start it but it will stop again. You can see it with docker ps -a.
The accepted answer in that question is very old and not very good. If you run that command on the current Docker version you get an error No command specified!
What you need to do is tell that container to run a command:
docker run ubuntu date
Will run a container from the image, run the date command, then exit. If you want to keep it running indefinitely, try something like:
docker run -d ubuntu tail -f /dev/null
You should see that the container is now running. The -d makes it run in the background, otherwise it will occupy your shell. And the final piece of the puzzle: since we have a container now that's configured to run a command, you can use docker ps to find its ID, and you can docker stop and docker start it at will.

How to restart a container on docker restart (--restart=true doesn't work)?

I am using docker version 1.1.0, started by systemd using the command line /usr/bin/docker -d, and tried to:
run a container
stop the docker service
restart the docker service (either using systemd or manually, specifying --restart=true on the command line)
see if my container was still running
As I understand the docs, my container should be restarted. But it is not. Its public facing port doesn't respond, and docker ps doesn't show it.
docker ps -a shows my container with an empty status:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
cb0d05b4e0d9 mildred/p2pweb:latest node server-cli.js - 7 minutes ago 0.0.0.0:8888->8888/tcp jovial_ritchie
...
And when I try to docker restart cb0d05b4e0d9, I get an error:
Error response from daemon: Cannot restart container cb0d05b4e0d9: Unit docker-cb0d05b4e0d9be2aadd4276497e80f4ae56d96f8e2ab98ccdb26ef510e21d2cc.scope already exists.
2014/07/16 13:18:35 Error: failed to restart one or more containers
I can always recreate a container using the same base image using docker run ..., but how do I make sure that my running containers will be restarted if docker is restarted. Is there a solution that exists even in case the docker is not stopped properly (imagine I remove the power plug from the server).
Thank you
As mentioned in a comment, the container flag you're likely looking for is --restart=always, which will instruct Docker that unless you explicitly docker stop the container, Docker should start it back up any time either Docker dies or the container does.

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