Specifying environment variables - Amazon Elastic Container Service
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Specifying environment variables


We recommend storing your sensitive data in either Amazon Secrets Manager secrets or Amazon Systems Manager Parameter Store parameters. For more information, see Specifying sensitive data.

Environment variables specified in the task definition are readable by all IAM users and roles that are allowed the DescribeTaskDefinition action for the task definition.

Environment variable files are objects in Amazon S3 and all Amazon S3 security considerations apply. See the below section Required IAM permissions.

Environment variables can be passed to your containers in the following ways:

  • Individually using the environment container definition parameter. This maps to the --env option to docker run.

  • In bulk, using the environmentFiles container definition parameter to list one or more files containing the environment variables. The file must be hosted in Amazon S3. This maps to the --env-file option to docker run.

Specifying environment variables in a file enables you to bulk inject environment variables as opposed to specifying them individually. Within your container definition, specify the environmentFiles object with a list of Amazon S3 buckets containing your environment variable files. The files must use an .env file extension and there is a limit of ten files per task definition.

We do not enforce a size limit on the environment variables, but a large environment variables file might fill up the disk space. Each task that uses an environment variables file causes a copy of the file to be downloaded to disk. We remove the file as part of the task cleanup.

The following is a snippet of a task definition showing how to specify individual environment variables.

{ "family": "", "containerDefinitions": [ { "name": "", "image": "", ... "environment": [ { "name": "variable", "value": "value" } ], ... } ], ... }

The following is a snippet of a task definition showing how to specify an environment variable file.

{ "family": "", "containerDefinitions": [ { "name": "", "image": "", ... "environmentFiles": [ { "value": "arn:aws:s3:::s3_bucket_name/envfile_object_name.env", "type": "s3" } ], ... } ], ... }

Considerations for specifying environment variable files

The following should be considered when specifying an environment variable file in a container definition.

  • For Amazon ECS tasks on Amazon EC2, your container instances require version 1.39.0 or later of the container agent to use this feature. For information about checking your agent version and updating to the latest version, see Updating the Amazon ECS container agent.

  • For Amazon ECS tasks on Amazon Fargate, your tasks must use platform version 1.4.0 or later (Linux) to use this feature. For more information, see Amazon Fargate platform versions.

    Verify that the variable is supported for the operating system platform. For more information, see Container definitions and Other task definition parameters.

  • The file must use the .env file extension and UTF-8 encoding.

  • Each line in an environment file should contain an environment variable in VARIABLE=VALUE format. Spaces or quotation marks are included as part of the values. Lines beginning with # are treated as comments and are ignored. For more information on the environment variable file syntax, see Declare default environment variables in file.

    The following is an example showing the syntax that must be used.

    #This is a comment and will be ignored VARIABLE=VALUE ENVIRONMENT=PRODUCTION
  • If there are environment variables specified using the environment parameter in a container definition, they take precedence over the variables contained within an environment file.

  • If multiple environment files are specified and they contain the same variable, they are processed in order of entry. This means that the first value of the variable is used and subsequent values of duplicate variables are ignored. We recommend that you use unique variable names.

  • If an environment file is specified as a container override, it is used, and any other environment files specified in a container definition is ignored.

Required IAM permissions

The Amazon ECS task execution role is required to use this feature. This allows the container agent to pull the environment variable file from Amazon S3. For more information, see Amazon ECS task execution IAM role.

To provide access to the Amazon S3 objects that you create, manually add the following permissions as an inline policy to the task execution role. Use the Resource parameter to scope the permission to the Amazon S3 buckets that contain the environment variable files. For more information, see Adding and Removing IAM Policies.

  • s3:GetObject

  • s3:GetBucketLocation

An example inline policy adding the permissions is shown.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "s3:GetObject" ], "Resource": [ "arn:aws:s3:::examplebucket/folder_name/env_file_name" ] }, { "Effect": "Allow", "Action": [ "s3:GetBucketLocation" ], "Resource": [ "arn:aws:s3:::examplebucket" ] } ] }