RedisConnectionException: Unable to connect to localhost:6379

The RedisConnectionException is an error that occurs when a Redis client is unable to establish a connection with the Redis server. In this particular case, the error message indicates that the client was unable to connect to the Redis server running on the localhost (i.e., the same machine as the client) on port 6379.

There are several reasons why this error might occur. Some possible causes include:

- The Redis server is not running or is not listening on the specified port.
- The Redis server is running, but is not configured to accept connections from the client's IP address or network.
- There is a firewall or security setting that is blocking the client's connection to the Redis server.
- There is a network connectivity issue between the client and the server.

To troubleshoot this error, you may want to try the following steps:

- Verify that the Redis server is running and is listening on the correct port by using the redis-cli command-line tool or a Redis GUI client to connect to the server.
- Check the Redis server's configuration file to ensure that it is configured to accept connections from the client's IP address or network.
- Verify that there are no firewall or security settings that are blocking the client's connection to the Redis server.
- Check the network connectivity between the client and the server by using tools such as ping, traceroute, or telnet to test the connection.

If none of these steps resolve the issue, you may need to consult with a Redis expert or system administrator for further assistance.