This is not an all-inclusive list, any environment variablec an be passed to the Docker image.
Variables like POSTGRES_USER and POSTGRES_PASSWORD can be passed through in order to connect to the database with a specific username & password.
AIRBRAKE_API_KEY
AIRBRAKE_PROJECT_ID
BITCOIN_NETWORK
BITCOIN_PUB_KEY
BLOCK_CYPHER_CALLBACK_URL
BLOCK_CYPHER_KEY
BUNDLE_GEMFILE
COORDINATOR_CLIENT_KEY
COORDINATOR_CLIENT_SECRET
COORDINATOR_CLIENT_URL
DATABASE_URL
EMAIL_DOMAIN
EMAIL_USERNAME
ETHEREUM_ACCOUNT
ETHEREUM_DEFAULT_GAS_LIMIT
ETHEREUM_EXPLORER_URL
ETHEREUM_EXTERNAL_HEIGHT_URL
ETHEREUM_GAS_PRICE_INCREASE
ETHEREUM_MINIMUM_BALANCE
ETHEREUM_URL
HEALTH_CHECK_TIME
LOG_LEVEL
MAX_THREADS
NODE_NAME
NOTIFICATION_EMAIL
PORT
PRIVATE_KEY_PASSWORD
RAILS_ENV
RAILS_SERVE_STATIC_FILES
remote
SECRET_KEY_BASE
CHAINLINK_PORT
SOLIDITY_URL
WEB_CONCURRENCY
WEI_WATCHERS_PASSWORD
WEI_WATCHERS_URL