Conatiner ID while building dockerfile.
I am building my own dockerfile. While building dockerfile using docker build . command I saw that it executes every command that was written in dockerfile. But while executing it displays a message Running in some container ID for every command written in dockerfile and also the ID changes for every command.
Are the containers changing for each and every command or the ID of same container changes as it also gets stop after every command execution
See the attached image and the highlighted text.
Docker more or less acts like it runs docker run and docker commit for each line in the Dockerfile. Containers never get reused; each line is a new container.
The other corollary to this is that the line after Removing intermediate container ... is a valid image ID, so one useful way to debug a build is to docker run a15a9b plugging in one of those intermediate image IDs.
Related
After I make any code change, my typical development steps are:
Change code and build the jar file
Build docker image that consumes the jar file
Kill current "docker-compose up" command.
Run "docker-compose up" again.
My docker-compose file has five services. On step 3, all the containers go down. Ideally, I just need to re-run my app container.
I am looking for a way to do the following in a batch script:
Bring down the app container. The other four containers should continue to run.
Build a new docker image
Force docker-compose to recreate my app container and start it.
For step 1, looks like I can use "docker-compose kill myappname."
Step 2 is also straightforward.
I am wondering how I can accomplish step 3. Thanks.
You don't need to stop the current container explicitly.
If your image has changed, docker compose will recognize it and recreate your container, when you run the up command again.
So, rebuild your image and run docker compose up.
If you use compose to build the image, add the --build flag to let it rebuild your image, after which the container is also recreated.
You cann also add the name off a specific service to your up command, i.e. docker compose up -d --build app
If the image hasnt changed, you cann add the --force-recreate flag.
Is it correct to say that whenever I use the command FROM in a Dockerfile, the docker build process creates a new container where the subsequent commands run?
If not, can you please provide a more accurate description?
I am new to docker, and have downloaded the tfx image using
docker pull tensorflow/tfx
However, I am unable to find anywhere how to successfully launch a container for the same.
here's a naive attempt
You can use docker image ls to get a list of locally-built Docker images. Note that an "image" is a template for a VM.
To instantiate the VM and shell into it, you would use a command like docker run -t --entrypoint bash tensorflow/tfx. This spins up a temporary VM based on the tensorflow/tfx image.
By default, Docker assumes you want the latest version of that image stored on your local machine, i.e. tensorflow/tfx:latest in the list. If you want to change it, you can reference a specific image version by name or hash, e.g. docker run -t --entrypoint bash tensorflow/tfx:1.0.0 or docker run -t --entrypoint bash fe507176d0e6. I typically use the docker image ls command first and cut & paste the hash, so my notes can be specific about which build I'm referencing even if I later edit the relevant Dockerfile.
Also note that changes you make inside that VM will not be saved. Once you exit the bash shell, it goes away. The shell is useful for checking the state & file structure of a constructed image. If you want to edit the image itself, use a Dockerfile. Each line of a Dockerfile creates a new image when the Dockerfile is compiled. If you know that something went wrong between lines 5 and 10 of the Dockerfile, you can potentially shell into each of those images in turn (with the docker run command I gave above) to see what went wrong. Kinda tedious, but it works.
Also note that docker run is not equivalent to running a TFX pipeline. For the latter, you want to look into the TFX CLI commands or otherwise compile the pipeline - and probably upload it to an external Kubeflow server.
Also note that the Docker image is just a starting point for one piece of your TFX pipeline. A full pipeline will require you to specify the components you want, a more-complete Dockerfile, and more. That's a huge topic, and IMO, the existing documentation leaves a lot to be desired. The Dockerfile you create describes the image which will be distributed to each of the workers which process the full pipeline. It's the place to specify dependencies, necessary files, and other custom setup for the machine. Most ML-relevant concerns are handled in other files.
I am confused with some terms.
Is Dockerile designed to create an image or a set of instruction of how to create a container from an image?
Because there are command e.g. FROM (to get the base image), RUN (To run executable in the container) etc. These command looks like an instruction to how to create the container.
Docker images are static, and are built from the instructions specified in the Dockerfile. They use Union File-System (UnionFS), so that the changes made when building an image are stacked on top of each other, generating a DAG (Directed Acyclic Graph) of build history. The FROM directive at the top of the Dockerfile simply points to an existing image, and starts building on top of that.
A container is simply an instantiated version of an image, basically just this UnionFS with a read/write layer dropped on top of it.
Interestingly, if you watch the output when you run docker build (in a directory with a Dockerfile) you'll see that what is happening is each instruction starts up a container based on the current state of the image, runs the command (apt-get install ... or whatever) and then commits that change to the image. That's why it's good to batch up commands in a Dockerfile - because each one will start a new container.
Dockerfile is used to create an image which you can later use to create a container using docker build.
From the docs
Docker can build images automatically by reading the instructions from a Dockerfile. A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build users can create an automated build that executes several command-line instructions in succession.
Also RUN will instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Dockerfile and not "Run (To run executable in the container)". For details see this.
Image:
Docker engine use Dockerfile reference to build up Image from Dockerfile instruction like (FROM, RUN etc.)
Container:
Docker engine start container from Image and we can say Container is RUN time instance of Image
If I want to run a python script in my container what is the point in having the RUN command, if I can pass in an argument at build along with running the script?
Each time I run the container I want x.py to be run on an ENV variable passed in during the build stage.
If I were to use Swarm, and the only goal was to run the x.py script, swarm would only be building nodes, rather than building and eventually running, since the CMD and ENTRYPOINT instructions only happen at run time.
Am I missing something?
The docker build command creates an immutable image. The docker run command creates a container that uses the image as a base filesystem, and other metadata from the image is used as defaults to run that image.
Each RUN line in a Dockerfile is used to add a layer to the image filesystem in docker. Docker actually performs that task in a temporary container, hence the selection of the confusing "run" term. The only thing preserved from that RUN command are the filesystem changes, running processes, changes to environment variables, shell settings like the current working directory, are all lost when the temporary container is cleaned up at the completion of the RUN command.
The ENTRYPOINT and CMD value are used to specify the default command to run when the container is started. When both are defined, the result is the value of the entrypoint is run with the value of the cmd appended as a command line argument. The value of CMD is easily overridden at the end of the docker run command line, so by using both you can get easy to reconfigure containers that run the same command with different user input parameters.
If the command you are trying to run needs to be performed every time the container starts, rather than being stored in the immutable image, then you need to perform that command in your ENTRYPOINT or CMD. This will add to the container startup time, so if the result of that command can be stored as a filesystem change and cached for all future containers being run, you want to make that setting in a RUN line.