I'm running an application under development with docker-compose.
I have a "web" service running a python Flask web application. This service depends on other ones (database, cache, ...).
I need to run the "web" main service interactively in order to get access to a debugger (ipdb).
I found out that the way to do this would be
docker-compose run --name my-app.web --service-ports web
When I exit this container and try to run it again with the same command I got this error:
ERROR: Cannot create container for service web: Conflict. The container name "/my-app.web" is already in use by container "4fed84779bb02952dedb8493a65bd83b1a6664f066183233e8c8b4dc62291643". You have to remove (or rename) that container to be able to reuse that name.
How can I start again this container without creating a new one ?
Or is it the correct way to create new containers each time I need to start this application ?
Or did I miss something to be able to start one of the service interactively ?
As you're setting a custom name, docker-compose run doesn't remove the container once the execution is completed. To enable this behavior use the option --rm:
docker-compose run --rm --name my-app.web --service-ports web
You can also remove the container manually to be able to run it again:
docker rm my-app.web
This is not necessary if you don't set a custom name.
Related
I have an docker container running prometheus and sometimes I have to update an config file inside the container, the problem is that I don't know who I can update this file without deleting and creating the container again.
docker run --network="host" -d --name=prometheus -p 9090:9090 -v ~/prometheus.yaml:/etc/prometheus/prometheus.yml prom/prometheus --config.file=/etc/prometheus/prometheus.yml
I want to know how I can update the prometheus.yaml without deleting and creating again the docker container.
You should VOLUME the data path of Prometheus outside of your container.
So if the container creates again, you can have your previous data.
The default data path of Prometheus is ./data but in docker it depends on your base-image.
In theory you can't since by principle containers are ephemeral. Meaning they're supposed to be disposable upon exiting. However, there are a few ways out of your predicament:
#1. Create a new Image from your running container: https://www.scalyr.com/blog/create-docker-image/ to persist the state.
#2. Copy your data from within the container to the "outside world" as a backup, if option 1 is not the right option for you (here's an explanation how to do so: https://linuxhandbook.com/docker-cp-example/). You could also log in to the container (docker exec -it <container-name> bash) and then use yum or apt install (depending on your base image) to install the necessary tools to make your backup (rsync, ...), if the sometimes very barebones baseimage does not provide these.
#3. As #Amir already mentioned, you should always create a Volume inside your Container and map it to the outside world to have a persistent data storage. You create a Volume by the VOLUME-Keyword in the Dockerfile: https://docs.docker.com/storage/volumes/ ..by doing so you can restart the container everytime if the config changes without worrying about data loss.
HTH
Use the reload url
Prometheus can reload its configuration at runtime. If the new configuration is not well-formed, the changes will not be applied. A configuration reload is triggered by sending a SIGHUP to the Prometheus process or sending a HTTP POST request to the /-/reload endpoint (when the --web.enable-lifecycle flag is enabled). This will also reload any configured rule files.
Use the following the change the config inside the container using:
docker exec -it <container_name> sh
Map the config to outside the docker container for persistence using
-v <host-path>:<container_path>
As everyone knows, we can use docker start [dockerID] to start a closed container.
But, If this container exits immediately after startup. What should I do?
For example, I have a MySQL container, it runs without any problems. But the system is down. At next time I start this container. It tell me a file is worry so that this container immediately exit.
Now I want to delete this file, but this container can not be activated, so I can't enter this container to delete this file. What should I do?
And if I want to open bash in this state container, What should I do?
Delete the container and launch a new one.
docker rm dockerID
docker run --name dockerID ... mysql:5.7
Containers are generally treated as disposable; there are times you're required to delete and recreate a container (to change some networking or environment options; to upgrade to a newer version of the underlying image). The flip side of this is that containers' state is generally stored outside the container filesystem itself (you probably have a docker run -v or Docker Compose volumes: option) so it will survive deleting and recreating the container. I almost never use docker start.
Creating a new container gets you around the limitations of docker start:
If the container exits immediately but you don't know why, docker run or docker-compose up it without the -d option, so it prints its logs to the console
If you want to run a different command (like an interactive shell) as the main container command, you can do it the same as any other container,
docker run --rm -it -v ...:/var/lib/mysql/data mysql:5.6 sh
docker-compose run db sh
If the actual problem can be fixed with an environment variable or other setting, you can add that to the startup-time configuration, since you're already recreating the container
I have a container (i'm using this container https://hub.docker.com/_/mysql/) which had started before, with ID 5f96e9570d1b1475a888d7a615acdd9a7715c1ed6f0c40900f2e9c1ab485c7cf, but now how can i restart it ? I tried this command but not work
$ docker run --name mysql -e MYSQL_ROOT_PASSWORD=*Abcd1234 -d mysql:5.7
D:\CWindow10\Docker Toolbox\docker.exe: Error response from daemon: Conflict. The container name "/mysql" is already in use by container "5f96e9570d1b1475a888d7a615acdd9a7715c1ed6f0c40900f2e9c1ab485c7cf". You have to remove (or rename) that container to be able to reuse that name.
See 'D:\CWindow10\Docker Toolbox\docker.exe run --help'.
If i delete the container and retype the command, will the old data still exist in new container?
To restart an existing container, simply run docker start <container_name_or_id>.
Regarding the data: docker uses the concept of volumes to put data. For the mysql image, there's a section "Where to Store Data" on the docker hub site. If you don't manually declare where the image should go, docker will create one for you. If you want your data to be kept, the easiest way is to create a folder and tell the docker run command to map that volume. That way, you can still use it if you throw away your container.
use this command to restart container docker restart <CONTAINER>
starting new container will not preserve your data unless you have mounted external volume and stored data on it. Have a look at this blog http://blog.arungupta.me/docker-mysql-persistence/
In my Dockerfile I am trying to install multiple services and want to have them all start up automatically when I launch the container.
One among the services is mysql and when I launch the container I don't see the mysql service starting up. When I try to start manually, I get the error:
Failed to get D-Bus connection: Operation not permitted
Dockerfile:
FROM centos:7
RUN yum -y install mariadb mariadb-server
COPY start.sh start.sh
CMD ["/bin/bash", "start.sh"]
My start.sh file:
service mariadb start
Docker build:
docker build --tag="pbellamk/mariadb" .
Docker run:
docker run -it -d --privileged=true pbellamk/mariadb bash
I have checked the centos:systemd image and that doesn't help too. How do I launch the container with the services started using systemctl/service commands.
When you do docker run with bash as the command, the init system (e.g. SystemD) doesn’t get started (nor does your start script, since the command you pass overrides the CMD in the Dockerfile). Try to change the command you use to /sbin/init, start the container in daemon mode with -d, and then look around in a shell using docker exec -it <container id> sh.
Docker is designed around the idea of a single service/process per container. Although it definitely supports running multiple processes in a container and in no way stops you from doing that, you will run into areas eventually where multiple services in a container doesn't quite map to what Docker or external tools expect. Things like moving to scaling of services, or using Docker swarm across hosts only support the concept of one service per container.
Docker Compose allows you to compose multiple containers into a single definition, which means you can use more of the standard, prebuilt containers (httpd, mariadb) rather than building your own. Compose definitions map to Docker Swarm services fairly easily. Also look at Kubernetes and Marathon/Mesos for managing groups of containers as a service.
Process management in Docker
It's possible to run systemd in a container but it requires --privileged access to the host and the /sys/fs/cgroup volume mounted so may not be the best fit for most use cases.
The s6-overlay project provides a more docker friendly process management system using s6.
It's fairly rare you actually need ssh access into a container, but if that's a hard requirement then you are going to be stuck building your own containers and using a process manager.
You can avoid running a systemd daemon inside a docker container altogether. You can even avoid to write a special start.sh script - that is another benefit when using the docker-systemctl-replacement script.
The docker systemctl.py can parse the normal *.service files to know how to start and stop services. You can register it as the CMD of an image in which case it will look for all the systemctl-enabled services - those will be started and stopped in the correct order.
The current testsuite includes testcases for the LAMP stack including centos, so it should run fine specifically in your setup.
I found this project:
https://github.com/defn/docker-systemd
which can be used to create an image based on the stock ubuntu image but with systemd and multiuser mode.
My use case is the first one mentioned in its Readme. I use it to test the installer script of my application that is installed as a systemd service. The installer creates a systemd service then enables and starts it. I need CI tests for the installer. The test should create the installer, install the application on an ubuntu, and connect to the service from outside.
Without systemd the installer would fail, and it would be much more difficult to write the test with vagrant. So, there are valid use cases for systemd in docker.
I created a data only container containing static HTML files that are intended to be consumed by a nginx container. Goal is that my webapp is providing a volume that nginx can use.
For this reason I created a simple Dockerfile:
FROM scratch
MAINTAINER me <me#me.com>
ADD dist/ /webappp/
When I run the created container from command line run -d -v /webappp --name webapp myOrg/webapp echo yo
I get the error Error response from daemon: Cannot start container db7fd5cd40d76311f8776b1710b4fe6d66284fe75253a806e281cd8ae5169637: exec: "echo": executable file not found in $PATH which if of course correct because the image has no commands at all the can be executed. Running a container without a command is not possible.
While this error on command line is not a big problem for me because I know the data container is still created and can now be accessed by nginx it turns out to be a no go if I want to automate it with Vagrant. The automated processes always fail because of this error.
My only solution so far is to extend my little handy image from from a distro which IMHO doesn't make sense for a data only container in order just to call echo or true!
Is there a NOP exec command in docker or does docker need always to execute something, is it possible to run a scratch container that does nothing or does not produce an error.
As mentioned in the Docker manual: The container don't need to be running. It also doesn't say that the container "should" be able to run at all.
So instead of echoing something stupid by running a data only container e.g. docker run -v /webappp --name webapp myOrg/webapp echo yo
It is already enough to just create the container and never run/start it.
docker create -v /webappp --name webapp myOrg/webapp
Note to self: Vagrant does not support docker create when provisioning!
Why are you using scratch?
Just use the nginx image as a base. You already have the image cached so it won't take up any more space and you'll be able to call echo.
Some references for data containers:
Data-only container madness
Understanding Volumes in Docker
Offiical docs on data containers