redis.exceptions.AuthenticationError: Authentication required

TL;DR: The server requires a password and you did not send one. Pass your password via the password argument of redis.Redis (and your username via the username argument if the server uses ACLs).

redis.exceptions.AuthenticationError: NOAUTH Authentication required.

Fix it

1. Confirm the server requires auth: redis-cli ping. Expected: NOAUTH Authentication required.
2. Provide the password value build the client as redis.Redis with host [host], port 6379, and your password supplied through the password argument. Expected: r.ping() returns True.
3. Redis 6+ ACLs: also pass username=[your username]. Expected: authenticated as that user.
4. Or via URL: redis.from_url() with a URL that carries your password in the userinfo section before [host]:6379/0. Expected: connects.

When this applies

• The error is NOAUTH Authentication required.

When it doesn't

• WRONGPASS: you sent a password but it is wrong; fix the value.
• Connection refused: the server is not reachable at all.

Compatibility

• redis-py 3.x/4.x/5.x; Redis 5 (requirepass) and 6+ (ACLs).

Why it happens

A server with requirepass or ACLs rejects every command until AUTH succeeds. Clients default to no password, so any secured server 401s them immediately.

Edge cases

• Special characters in the password must be URL-encoded in from_url strings.
• In from_url, the empty username slot matters: put a colon before the password in the userinfo section; omitting the colon parses differently.