I am trying to learn docker practically. To start with I have created a simple .net core 3.1 console application. This application simply writes a message in a text file in a specific location. I have created a docker image from it and then docker container from the image. When I run the docker container, it runs and stops successfully.
The docker file:
FROM mcr.microsoft.com/dotnet/aspnet:3.1
COPY bin/Release/netcoreapp3.1/publish App/
WORKDIR /App
ENTRYPOINT ["dotnet", "ConsoleApp1.dll"]
I also checked the logs using command "docker logs container_id". But it returns nothing.
Am I missing anything?
Docker runs a process inside a container, when that process ends the container stops and end too. As the process in your container only writes something and exits, the container exits and stops too.
Also the text file is written in the container file system. So you will not be able to see it in your host, unless you use a volume. Try printing the string to standard output instead
Related
I was asked to build an image for python programs and for example if we create 3 python programs and create a an image for them and if we run that image, basically a container will be created and will execute and will exit, and for the second program another container will be created.
that's what usually will happen. but here i was informed that a single container should be created for all the programs and it should be in the run state continuously and if we give the program name in the run command it should execute that program, not the other two programs, and it should start and stop based on the commands i give.
for this to happen i was given a hint/suggestion i should say that if i create an entrypoint script and copy that in the docker file it'll work. but unfortunately, when i researched on it in internet the entrypoint scripts are available for linux, but I'm using windows here.
So, first to explain why the container exits after you run it: Containers are not like VMs. Docker (or the container runtime you choose) will check for what is running on the containers. This "what is running" is defined on the ENTRYPOINT on your dockerfile. If you don't have an entrypoint, there's nothing running and Docker stops the containers. Or it might be the case that something ran and the container stopped after it executed.
Now, the Windows Server base images don't have an entrypoint. If you just ask to run the container, it will start and stop immediately. That is a problem for background services like web servers, for example IIS. To solve that, Microsoft created a service called Service Monitor. If you look for the docker file of the IIS image that Microsoft produces, you'll notice that the entrypoint is the service monitor that in turn checks the status of the IIS service. If IIS is running, service monitor will continue to run and thus the container keeps running indefinitely. (Here's the dockerfile: https://github.com/Microsoft/iis-docker/blob/main/windowsservercore-ltsc2022/Dockerfile)
Now, for your case, what you need is a job on your python container. Look at the description on the link provided by Mihai: https://hub.docker.com/_/python
This is their example docker file:
FROM python:3
WORKDIR /usr/src/app
COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
CMD [ "python", "./your-daemon-or-script.py" ]
Note the last line. It's not an entry point, which means that the python app will run and exit, which will stop the container. IF you need the container to run indefinetly, either you leverage something like service monitor (but need to build a service in the background) or you create your own logic to keep something running. For example, a infinte loop.
Does that helps?
I am working with Golang application that saves the information inside sqlite file and that resideds inside the data/sqlite.db same directory as docker file. My docker file is something like this
p.s: guys it's my very first docker file please be kind to me :(
FROM golang:1.16.4
ENV GIN_MODE=release
ENV PORT=8081
ADD . /go/src/multisig-svc
WORKDIR /go/src/multisig-svc
RUN go mod download
RUN go build -o bin/multisig-svc cmd/main.go
EXPOSE $PORT
ENTRYPOINT ./bin/multisig-svc
I deployed this application to the Google cloud plateform but somehow the container gets restarted there and after that my db is vanished. So i researched and try to use volumes.
I build the container using this command docker build -t svc . and then run it with docker run -p 8080:8081 -v data:/var/dump -it svc but i can not see the data folder is getting copied to /var/dump directory. My basic idea is , Whenever the container start it loads the db file from dump and then past it to data directory so application can use it and when it exits it copy it back to dump directory. I don't know if i am on right track any help would really be appreciated.
#Edit
The issue is when no request arrives for 15 minutes GPC shut down the container and start it when there comes a request again. Now the issue is to somehow fetch the db file from dump directory update it and write it back to the dump dir when container goes down for future use.
For a local run and if you are running on a VM, you need to specify the absolute path of the directory you want to mount as a bind mount into your directory. In this case something like that should work
docker run -p 8080:8081 -v $(pwd)/data:/var/dump -it svc
When you don't specify the absolute path, the volume you're mounting to your running container is a named volume manage by the docker daemon. And it is not located in a path related to your current working directory. You can find more information about how work docker volumes here https://docs.docker.com/storage/volumes/
However there are multiple environment on GCP (app engine, kubernetes, VMs), so depending on your environment you may need to adapt this solution.
Due to a number of circumstances beyond my control that I cannot change, the task arose to update the java script in the running container. A .net core site is running in the container. I have successfully changed the script in the wwwroot folder, but these changes are not available to clients. I did "docker restart cont_id" and "kill-HUV 1" inside the container, but it didn't help. Can I somehow update the script without stopping the container? Here is the docker file:
FROM mcr.microsoft.com/dotnet/core/aspnet:2.2.4
COPY . /app
WORKDIR /app
ENV ASPNETCORE_URLS http://+:80
EXPOSE 80
CMD [ "dotnet", "ххх.WebUi.dll" ]
You need to docker build a new image, docker stop && docker rm the existing container, and docker run a new container on the new image. You can rebuild the image while the old container is still running, but there's no way to cause the existing container to somehow "switch" to a different image.
There are a number of options that can only be set when you initially build a container; not just the image to use (and the versions of language runtimes and support libraries embedded in that image) but also port mappings, environment variable settings, volume mounts, and others. Deleting and recreating a container in this way is extremely routine. Tools like Docker Compose will let you write the container's settings into a file, so it's straightforward to recreate a container when needed.
I built myself an image for ROS. I run it while mounting my original home on the host and some tricks to get graphics as well. After starting the shell inside docker I always need to execute two source commands. One of the files to be sourced are actually inside the container, but the other resides in my home, which only gets mounted on starting the container. I would have these two files sourced automatically.
I tried adding
RUN bash -c "source /opt/ros/indigo/setup.bash"
to the image file, but this did not actually source it. Using CMD instead of run didn't drop me into the container's shell (I assume it finished executing source and then exited?). I don't even have an idea how to source the file that is only available after startup. What would I need to do?
TL;DR: you need to perform this step as part of your CMD or ENTRYPOINT, and for something like a source command, you need a step after that in the shell to run your app, or whatever shell you'd like. If you just want a bash shell as your command, then put your source command inside something like your .bashrc file. Or you can run something like:
bash -c "source /opt/ros/indigo/setup.bash && bash"
as your command.
One of the files to be sourced are actually inside the container, but the other resides in my home, which only gets mounted on starting the container.
...
I tried adding ... to the image file
Images are built using temporary containers that only see your Dockerfile instructions and the context sent with that to run the build. Containers use that built image and all of your configuration, like volumes, to run your application. There's a hard divider between those two steps, image build and container run, and your volumes are not available during that image build step.
Each of those RUN steps being performed for the image build are done in a temporary container that only stores the output of the filesystem when it's finished. Changes to your environment, a cd into another directory, spawned processes or services in the background, or anything else not written to the filesystem when the command spawned by RUN exits, will be lost. This is one reason you will see commands chained together in a single long RUN command, and it's why you have ENV and WORKDIR commands in the Dockerfile.
I'm running a docker container with a volume /var/my_folder. The data there is persistent: When I close the container it is still there.
But also want to have the data available on my host, because I want to work on code with an IDE, which is not installed in my container.
So how can I have a folder /var/my_folder on my host machine which is also available in my container?
I'm working on Linux Mint.
I appreciate your help.
Thanks. :)
Link : Manage data in containers
The basic run command you want is ...
docker run -dt --name containerName -v /path/on/host:/path/in/container
The problem is that mounting the volume will, (for your purposes), overwrite the volume in the container
the best way to overcome this is to create the files (inside the container) that you want to share AFTER mounting.
The ENTRYPOINT command is executed on docker run. Therefore, if your files are generated as part of your entrypoint script AND not as part of your build THEN they will be available from the host machine once mounted.
The solution is therefore, to run the commands that creates the files in the ENTRYPOINT script.
Failing this, during the build copy the files to another directory and then COPY them back in your ENTRYPOINT script.