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Revisiting of Environmental variables precendence (#15396)
* Rewriting based on knowledge transfer * Fix and minor edits
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---
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title: Environment variables precedence
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description: TODO
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description: Scenario Overview illustrating how environmental variables are resolved in Compose
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keywords: compose, environment, env file
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---
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<style>
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div {
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color: RoyalBlue;
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}
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table {
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font-family: monospace;
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}
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</style>
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## Order of precedence
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1. Passed from the command-line [`docker compose run --env <KEY[=VAL]>`](../../engine/reference/commandline/compose_run/#options).
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2. Passed from/set in `compose.yaml` service's configuration, [from the environment key](../../compose/compose-file/#environment).
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3. Passed from/set in `compose.yaml` service's configuration, [from the env_file key](../../compose/compose-file/#env_file).
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4. Passed from/set in Container Image [in ENV directive](../../engine/reference/builder/#env).
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- Command Line (docker compose run --env <KEY[=VAL]> https://docs.docker.com/engine/reference/commandline/compose_run/#options)
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- Compose File (service::environment section: https://docs.docker.com/compose/compose-file/#environment)
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- Compose File (service::env_file section file: https://docs.docker.com/compose/compose-file/#env_file)
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- Container Image ENV directive (https://docs.docker.com/engine/reference/builder/#env)
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### Precedence quick overview table
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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.
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When `WHEREAMI` is the variable in case:
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Each row represents a scenario and each columns represents a context where you can be setting or passing an environment variable.
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| Image (`ENV` directive in Dockerfile) | OS Environment | `.env` file on the project root (or overwrite through `docker compose -–env-file <FILE>`) | Compose file (`service::env_file`) | Compose file (`service::environment`) | Command line (docker compose run -e <KEY[=VAL]>) | RESULT |
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|:-------------------------------------:|:-----------------:|:-----------------------------------------------------------------------------------------:|:----------------------------------:|:-----------------------------------------:|:------------------------------------------------:|:------------------------:|
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| <div>Dockerfile</div> | OS_Env | WHEREAMI=DotEnv_File | | | | Dockerfile |
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| Dockerfile | OS_Env | WHEREAMI=<div>DotEnv_File</div> | | | WHEREAMI | DotEnv_File |
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| Dockerfile | <div>OS_Env</div> | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | | WHEREAMI | OS_Env |
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| <div>Dockerfile</div> | OS_Env | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | | | Dockerfile |
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| Dockerfile | | WHEREAMI=${WHEREAMI:-<div>DotEnv_File_DefaultValue</div>} | | | WHEREAMI | DotEnv_File_DefaultValue |
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| Dockerfile | OS_Env | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | | WHEREAMI=<div>Command_Line</div> | Command_Line |
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| Dockerfile | <div>OS_Env</div> | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | WHEREAMI | | OS_Env |
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| Dockerfile | OS_Env | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | WHEREAMI=<div>Environment_Section</div> | | Environment_Section |
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| Dockerfile | OS_Env | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | WHEREAMI=Environment_Section | WHEREAMI=<div>Command_Line</div> | Command_Line |
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| Dockerfile | <div>OS_Env</div> | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | WHEREAMI=Environment_Section | WHEREAMI | OS_Env |
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| Dockerfile | OS_Env | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | WHEREAMI | WHEREAMI=<div>Command_Line</div> | Command_Line |
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| Dockerfile | OS_Env | | WHEREAMI=Env_File | | WHEREAMI=<div>Command_Line</div> | Command_Line |
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| Dockerfile | OS_Env | | WHEREAMI=Env_File | WHEREAMI=<div>Environment_Section</div> | | Environment_Section |
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| Dockerfile | OS_Env | | WHEREAMI=<div>Env_File</div> | | | Env_File |
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| Dockerfile | <div>OS_Env</div> | | | WHEREAMI=${WHEREAMI:-Environment_Section} | | OS_Env |
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| Dockerfile | <div>OS_Env</div> | WHEREAMI=${WHEREAMI:-DotEnv_File_DefaultValue} | | WHEREAMI=${WHEREAMI:-Environment_Section} | | OS_Env |
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| # | `.env` file | `compose.yaml`:`env_file` key | `compose.yaml`:`environment` key | CMD | Image | OS | Resolved as |
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|:-:|:--------------------------:|:-----------------------------:|:---------------------------------:|:------------:|:-------------:|:------------:|:-----------------:|
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| 1 | `TAG=1.3` | Unset | Unset | - | `TAG=1.6` | `TAG=1.4` | `TAG=1.6` |
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| 2 | `TAG=1.3` | Unset | Unset | `TAG` | `TAG=1.6` | `TAG=1.4` | `TAG=1.3` |
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| 3 | `TAG=$TAG:-1.2` | Unset | Unset | `TAG` | `TAG=1.6` | `TAG=1.4` | `TAG=1.4` |
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| 4 | `TAG=$TAG:-1.2` | Unset | Unset | - | `TAG=1.6` | `TAG=1.4` | `TAG=1.6` |
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| 5 | `TAG=$TAG:-1.2` | Unset | Unset | `TAG` | `TAG=1.6` | - | `TAG=1.6` |
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| 6 | `TAG=$TAG:-1.2` | Unset | Unset | `TAG=1.5` | `TAG=1.6` | `TAG=1.4` | `TAG=1.5` |
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| 7 | `TAG=$TAG:-1.2` | Unset | `TAG` | - | `TAG=1.6` | `TAG=1.4` | `TAG=1.4` |
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| 8 | `TAG=$TAG:-1.2` | Unset | `TAG=1.7` | `TAG` | `TAG=1.6` | `TAG=1.4` | `TAG=1.7` |
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| 9 | `TAG=$TAG:-1.2` | Unset | `TAG=1.7` | `TAG=1.5` | `TAG=1.6` | `TAG=1.4` | `TAG=1.5` |
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| 10| `TAG=$TAG:-1.2` | Unset | `TAG` | `TAG` | `TAG=1.6` | `TAG=1.4` | `TAG=1.4` |
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| 11| `TAG=$TAG:-1.2` | Unset | `TAG` | `TAG` | `TAG=1.6` | `TAG=1.4` | `TAG=1.4` |
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| 12| `TAG=$TAG:-1.2` | `TAG=1.8` | - | **`TAG=1.5`** | `TAG=1.6` | `TAG=1.4` | `TAG=1.5` |
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| 13| `TAG=$TAG:-1.2` | `TAG=1.8` | **`TAG=1.7`** | `TAG=1.5` | `TAG=1.6` | `TAG=1.4` | `TAG=1.7` |
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| 14| - |**`TAG=1.8`** | - | - | `TAG=1.6` | `TAG=1.4` | `TAG=1.8` |
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| 15| - | - | `TAG=1.7` | - | `TAG=1.6` | `TAG=1.4` | `TAG=1.4` |
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| 16| - | - | `TAG=1.7` | - | `TAG=1.6` | `TAG=1.4` | `TAG=1.4` |
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Description for each column:
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* Image - `ENV` directive in the Dockerfile
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* .env file - `.env` file on the project root (or, with higher precedence, the file passed via `docker compose -–env-file <FILE>`).
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* Command line - environmental variable passed via `docker compose run -e <KEY[=VAL]>`.
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* Compose file - in `environment` key from the service section in the `compose.yaml`.
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* Compose file - in `env_file key` from the service section in the `compose.yaml`.
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