Defining Environment Variables for Golem Agents

Environment variables in Golem can be set at multiple levels in the application manifest (golem.yaml) and via CLI parameters. They follow a cascade property system where values defined at lower (more specific) levels override or merge with values from higher (more general) levels.

Cascade Hierarchy (Most General → Most Specific)

componentTemplates → components → agents → presets

Each level can define env (a map of key-value pairs) and envMergeMode (how to combine with the parent level). More specific levels are applied on top of less specific ones.

1. Component Template Level

Define shared environment variables for all components that use a template:

componentTemplates:
  my-template:
    env:
      LOG_LEVEL: info
      SERVICE_NAME: my-service

All components referencing my-template via templates: [my-template] inherit these variables.

2. Component Level

Define or override environment variables for a specific component:

components:
  my-ns:my-component:
    templates: [my-template]
    env:
      DATABASE_URL: postgresql://localhost:5432/mydb
      LOG_LEVEL: debug   # overrides template's LOG_LEVEL

3. Agent Type Level

Define environment variables for a specific agent type within a component:

agents:
  MyAgent:
    env:
      CACHE_TTL: "300"
      FEATURE_FLAG: enabled

4. Preset Level (Component and Agent)

Both components and agents support presets that can add or override environment variables. Presets are selected at build/deploy time.

Component preset:

components:
  my-ns:my-component:
    env:
      LOG_LEVEL: info
    presets:
      debug:
        default: {}
        env:
          LOG_LEVEL: debug
          DEBUG_MODE: "true"
      release:
        env:
          LOG_LEVEL: warn

Agent preset:

agents:
  MyAgent:
    env:
      CACHE_TTL: "300"
    presets:
      debug:
        default: {}
        env:
          CACHE_TTL: "60"

Complete Multi-Level Example

componentTemplates:
  shared:
    env:
      LOG_LEVEL: info
      REGION: us-east-1
 
components:
  my-ns:my-component:
    templates: [shared]
    env:
      DATABASE_URL: postgresql://db:5432/app
    presets:
      debug:
        default: {}
        env:
          LOG_LEVEL: debug
 
agents:
  MyAgent:
    env:
      CACHE_TTL: "300"
      API_KEY: "{{ MY_API_KEY }}"
    presets:
      debug:
        default: {}
        env:
          CACHE_TTL: "60"

With the debug preset, the final resolved env for MyAgent would be:

Merge Modes

By default, environment variables from child levels are upserted (added or updated) into the parent map. You can change this per level with envMergeMode:

Example: Replace all inherited env vars

agents:
  MyAgent:
    envMergeMode: replace
    env:
      ONLY_THIS: "true"

Example: Remove specific inherited env vars

agents:
  MyAgent:
    envMergeMode: remove
    env:
      LOG_LEVEL: ""   # value is ignored, key is removed

Template Substitution in Values

Environment variable values support Jinja-style template substitution using {{ VAR_NAME }}. At deploy time, these are resolved against the host machine’s environment variables (the shell running golem deploy):

agents:
  MyAgent:
    env:
      API_KEY: "{{ MY_API_KEY }}"
      DB_PASSWORD: "{{ DB_PASSWORD }}"
      MIXED: "prefix-{{ SOME_VAR }}-suffix"

If a referenced host variable is missing, deployment fails with a clear error listing the missing variables. The substitution engine uses strict mode — all referenced variables must be defined.

Reading Environment Variables in Agent Code

Rust and TypeScript agents use the standard APIs to read environment variables (std::env::var in Rust, process.env in TypeScript).

Scala agents must use golem.wasi.Environment.getEnvironment() which returns a Map[String, String] of all environment variables via the WASI wasi:cli/environment@0.2.3 interface. Standard Scala sys.env does not work inside the WASM runtime. Example:

import golem.wasi.Environment
 
val env = Environment.getEnvironment()
val appMode = env.getOrElse("APP_MODE", "default")

Passing Env Vars to Individual Agent Instances via CLI

When creating an agent instance directly (outside golem deploy), you can pass environment variables with the --env / -e flag:

golem agent new 'MyAgent("instance-1")' \
  --env API_KEY=secret123 \
  --env LOG_LEVEL=debug

Multiple --env flags can be provided, each in KEY=VALUE format. These are set only on that specific agent instance and do not affect the manifest or other instances.

Summary of All Methods