diff --git a/.env.sample b/.env.sample
index 41f9b317..0635f724 100644
--- a/.env.sample
+++ b/.env.sample
@@ -114,3 +114,6 @@ HASHER_API_AZ_CLIENT_ID=
 HASHER_API_AZ_CLIENT_PASSWORD=
 HASHER_API_AZ_TENANT_ID=
 HASHER_API_AZ_KEY_VAULT_NAME=
+
+# ENV is used by Docker compose to separate runtime environments {dev|test|prod}.
+ENV=