As my chaincode will get execute on each chaincode container, I want to set environment variable inside every chaincode container so that i can use this environment variable in my chaincode.
I don't have access to create a chaincode container. It will get created automatically at the time of chaincode instantiation (one docker container per peer). So that i don't have any control to set the environment variable inside chaincode containers.
I also think to update and commit the chaincode containers, but if there are more endorsing peers then this could take unnecessary delay. So according to my understanding, the best way is to set the environment variable at the time of container creation.
Please let me know how to solve above problem?
You do not want to set an environment variable. If there is some type of "configuration" setting you need to pass into chaincode then you should pass it as a parameter to the Init function and then save the value using PutState and retrieve it using GetState as required.
If you want to set environment variables before running a container, use the --env argument for the docker run command:
$ docker run --help
...
-e, --env list Set environment variables
--env-file list Read in a file of environment variables
Use the -e, --env, and --env-file flags to set simple (non-array) environment variables in the container you’re running, or overwrite variables that are defined in the Dockerfile of the image you’re running. More info is here.
docker run -e MYVAR1 --env MYVAR2=foo --env-file ./env.list ubuntu bash
If you want to set environment variables after running a container, Docker does not allow this currently. See these issues:
https://github.com/moby/moby/issues/8838
https://github.com/moby/moby/issues/7561
Right now Docker can't change the configuration of the container once it's created, and generally this is OK because it's trivial to create a new container
Related
I have a running docker container using an ancestor my_base_image. Now when the container is running, can I set an environment variable using export command with docker exec? if yes, how?
I tried using the following, but doesn't work
docker exec -i -t $(docker ps -q --filter ancestor=`my_base_image`) bash -c "export my_env_var=hey"
Basically I want to set my_env_var=hey as env variable inside docker container. I know this can be done in may ways using .env_file or env key docker-compose & ENV in Dockerfile. But I just want to know if it is possible using docker exec command
This is impossible. A process can never change the environment of any other process beyond itself, except that it can specify the initial environment of processes it starts itself. In this case, your docker exec shell isn’t launching the main container process, so it can’t change that process’s environment variables.
This is one of a number of changes that you will need to stop, delete, and recreate the container for. You should treat this as extremely routine container maintenance and plan to delete the container eventually. That means, for example, keeping any data that needs to be persisted outside the container, ideally in an external database but possibly in a mounted volume.
I'm working on a dotnet core docker container (not aspnet), I'd like to specify configuration options for it through appsettings.json. These values will eventually be filled in through environment variables in kubernetes.
However, for local development, how do we easily pass in these settings without storing them in the container?
You can map local volumes to docker -v local_path:container_path.
If you gonna use kubernetes you can use ConfigMap as well.
You can pass env variables while running the container with -e flag of the command docker run.
With this method, you’ll have to pass each variable in the command line. For example, docker run -e VAR1=value1 -e VAR2=value2
If this gets cumbersome, you can write these values to an env file and use this file like so, docker run --env-file=filename
For reference, you can check out the official docs.
Is there a syntax to reference an environment variable from the host in a Docker env-file.
Specifically I'd like to do something like DOCKER_HOST=${HOSTNAME} where HOSTNAME would come the environment of the machine hosting the docker image.
The above doesn't get any attempt at replacement whatsoever and gets passed into the Docker image literally as ${HOSTNAME}.
This is generally not done at the image level, but at runtime, on docker run:
See "How to get the hostname of the docker host from inside a docker container on that host without env vars"
docker run .. -e HOST_HOSTNAME=$(hostname) ..
That does use an environment variable.
You can do so without environment variables, using -h
docker run -h=$(hostname)
But that does not work when your docker run is part of a docker compose. See issue 3840.
I am running a docker container using --env VAR="foo" to set a few variables. When I run commands on this running container from the same shell / environment that I started the container, everything is fine.
The problem is that now I want to run commands against this container from cron. When cron runs the same command, the ENV variables in the container no longer exist.
How can I persist these ENV variables in the container regardless of where it is accessed from?
Edit:
To clarify, I docker run from a standard shell. In the cron job, I use docker exec and that is when the ENV vars disappear.
I have also noticed that some host machines I can't do any exec's on docker containers from a cron job.
I presume you use docker run inside your cron task.
If that's the case that's normal. You are starting a new container from the same image.
If you want to use the same container (with all your env variables set), you can use docker exec.
https://docs.docker.com/reference/commandline/exec/
I've created a docker image for my database server and one for the web application. Using the documentation I'm able to link between both container using the environment variables as follow:
value="jdbc:postgresql://${DB_PORT_5432_TCP_ADDR}:${DB_PORT_5432_TCP_PORT}/db_name"
It works fine now but it would be better that the environment variables are more general and without containing a static port number. Something like:
value="jdbc:postgresql://${DB_URL}:${DB_PORT}/db_name"
Is there anyway to link between the environment variables? for example by using the ENV command in the dockerfile ENV DB_URL=$DB_PORT_5432_TCP_ADDR or by using the argument --env by running the image docker run ... -e DB_URL=$DB_PORT_5432_TCP_ADDR docker_image ?
Without building this kind of functionality into your docker startup shell scripts or other orchestration mechanism, this is not possible at the moment to create environment variables like you are describing here. You do mention a couple of workarounds. However, the problem at least with using the -e DB_URL=... in your docker run command is that your $DB_PORT_5432_TCP_ADDR environment variable is not known at runtime, and so you will not be able to set this value when you run it. Typically, this is what your orchestration layer is used for, service discovery and passing this kind of data among your containers. There is at least one workaround mentioned here on SO that involves constructing a special shell script that you put in your CMD or ENTRYPOINT directives that passes the environment variable to the container.