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I am trying to set an environment variable in the EC2 instance hosting ECS containers. The environment variable should be readable by the docker client on the EC2 instance at run time. I know it's possible to add userData like so: 

#!/bin/sh
echo export env_var=1 >> /etc/environment

But for some reason this env_var is not being picked up by the docker client when instantiating ECS tasks.

Any idea how I might go about doing this? Thanks in advance.

cyc115
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2 Answers2

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Are you simply adding environment variables? Then try the following

  1. Add variable in Dockerfile

    ARG DEV

    ENV DEV=${DEV}

  2. Add variable when build docker image

    docker build . -t projectname --build-arg DEV=False

byunghyun park
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  • thanks for suggesting. I would like the ECS docker client to pick up a host environment variable when it pulls a image from ECR as this example [here](https://docs.docker.com/engine/security/trust/trust_automation). Or an alternate solution would be to pass an `--disable-content-trust=false` flag when the ECS docker client runs `docker pull`. – cyc115 Sep 01 '17 at 14:43
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You can define environment variables from within the task definition that will get passed into your container using Docker's --env option. Advanced Container Definition Parameters (scroll down to "environment")

"environment" : [
    { "name" : "string", "value" : "string" },
    { "name" : "string", "value" : "string" }
]

Here's a quick sample of where how it looks on a full task definition:

{
    "family": "example-task",
    "containerDefinitions": [
        {
            "name": "sample-app",
            "image": "123456789012.dkr.ecr.us-west-2.amazonaws.com/aws-nodejs-sample:v1",
            "memory": 200,
            "cpu": 10,
            "essential": true,
            "environment": [
                {
                    "name": "ENVIRONMENT",
                    "value": "production"
                },
                {
                    "name": "API_HOST",
                    "value": "https://example.com"
                }
            ],
        }
    ]
}
John Veldboom
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  • Thanks @John for suggesting, but I am trying to pass a flag to the container daemon running the ECS containers (which I assume is docker) . Not to the running container – cyc115 Oct 02 '17 at 14:55