docker-docs/compose/envvars-precedence.md

title, description, keywords

title	description	keywords
Environment variables precedence	Scenario Overview illustrating how environmental variables are resolved in Compose	compose, environment, env file

Order of precedence

1. Passed from the command-line docker compose run --env <KEY[=VAL]>.
2. Passed from/set in compose.yaml service's configuration, from the environment key.
3. Passed from/set in compose.yaml service's configuration, from the env_file key.
4. Passed from/set in Container Image in ENV directive.

Precedence quick overview table

The table below provides a quick overview of how interpolation works when using all environment variables on Compose, using TAG, an environmental variable defining the version for an image, as an example.

Each row represents a scenario and each columns represents a context where you can be setting or passing an environment variable.

#	.env file	compose.yaml:env_file key	compose.yaml:environment key	CMD	Image	OS	Resolved as
1	TAG=1.3	Unset	Unset	-	TAG=1.6	TAG=1.4	TAG=1.6
2	TAG=1.3	Unset	Unset	TAG	TAG=1.6	TAG=1.4	TAG=1.3
3	TAG=$TAG:-1.2	Unset	Unset	TAG	TAG=1.6	TAG=1.4	TAG=1.4
4	TAG=$TAG:-1.2	Unset	Unset	-	TAG=1.6	TAG=1.4	TAG=1.6
5	TAG=$TAG:-1.2	Unset	Unset	TAG	TAG=1.6	-	TAG=1.6
6	TAG=$TAG:-1.2	Unset	Unset	TAG=1.5	TAG=1.6	TAG=1.4	TAG=1.5
7	TAG=$TAG:-1.2	Unset	TAG	-	TAG=1.6	TAG=1.4	TAG=1.4
8	TAG=$TAG:-1.2	Unset	TAG=1.7	TAG	TAG=1.6	TAG=1.4	TAG=1.7
9	TAG=$TAG:-1.2	Unset	TAG=1.7	TAG=1.5	TAG=1.6	TAG=1.4	TAG=1.5
10	TAG=$TAG:-1.2	Unset	TAG	TAG	TAG=1.6	TAG=1.4	TAG=1.4
11	TAG=$TAG:-1.2	Unset	TAG	TAG	TAG=1.6	TAG=1.4	TAG=1.4
12	TAG=$TAG:-1.2	TAG=1.8	-	TAG=1.5	TAG=1.6	TAG=1.4	TAG=1.5
13	TAG=$TAG:-1.2	TAG=1.8	TAG=1.7	TAG=1.5	TAG=1.6	TAG=1.4	TAG=1.7
14	-	TAG=1.8	-	-	TAG=1.6	TAG=1.4	TAG=1.8
15	-	-	TAG=1.7	-	TAG=1.6	TAG=1.4	TAG=1.4
16	-	-	TAG=1.7	-	TAG=1.6	TAG=1.4	TAG=1.4

Description for each column:

• Image - ENV directive in the Dockerfile
• .env file - .env file on the project root (or, with higher precedence, the file passed via docker compose -–env-file <FILE>).
• Command line - environmental variable passed via docker compose run -e <KEY[=VAL]>.
• Compose file - in environment key from the service section in the compose.yaml.
• Compose file - in env_file key from the service section in the compose.yaml.