Injected environment variables

A link sets the main variables below. When your code reads one of the also names instead of the main one, that name is set as well. Variables you set yourself always win. See How linking works.

Service	Main variables	Also
Postgres	DATABASE_URL	POSTGRES_URL, POSTGRES_URI, POSTGRESQL_URL, PG_URL, DB_URL, DATABASE_URI, DATABASE_CONNECTION_STRING
MySQL	DATABASE_URL, MYSQL_URL, MYSQL_HOST, MYSQL_PORT, MYSQL_USER, MYSQL_PASSWORD, MYSQL_DATABASE	DB_HOST, DB_PORT, DB_USER, DB_USERNAME, DB_PASSWORD, DB_PASS, DB_NAME, DB_DATABASE, DATABASE_HOST…
Valkey	REDIS_URL	VALKEY_URL, REDIS_URI, CACHE_URL, REDIS_CONNECTION_STRING
Object storage	S3_ENDPOINT, S3_PUBLIC_ENDPOINT, S3_REGION, S3_BUCKET, S3_ACCESS_KEY_ID, S3_SECRET_ACCESS_KEY, S3_FORCE_PATH_STYLE	AWS_ENDPOINT_URL, AWS_REGION, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_S3_BUCKET, BUCKET_NAME, S3_ENDPOINT_URL…
LiteLLM	OPENAI_BASE_URL, OPENAI_API_BASE, OPENAI_API_KEY, LLM_GATEWAY_URL	ANTHROPIC_BASE_URL, ANTHROPIC_API_KEY, LITELLM_URL, LITELLM_PROXY_URL, LITELLM_API_KEY, LLM_API_KEY
Secrets	Each key you added, under its own name
Observability	OTEL_EXPORTER_OTLP_ENDPOINT, OTEL_EXPORTER_OTLP_PROTOCOL, OTEL_SERVICE_NAME
Another app	<LABEL>_URL (its private address)

Apps built from code also get PORT, the port they should listen on.

Extra accounts and databases

On a link, Also inject adds another account’s variables with the account name as a suffix (DATABASE_URL_READONLY), and Also inject URLs for adds other Postgres databases as DATABASE_URL_<NAME>.

References

Your own variables can use ${label.field} for a linked node, and ${self.host} / ${self.url} for the app itself. Common fields: uri, host, port, user, password, name. zc describe kind <subtype> lists each service’s fields.