Inspect Redis commands using MONITOR

Eebs Kobeissi

I needed to check if the Redis client in our Rails application was namespacing keys correctly on certain commands. Instead of adding some debugging code on the Rails side to see what keys were being used, I chose to look at my local Redis server instead. If I saw any key without the app:development prefix, I knew the issue was still present.

Using the MONITOR command and the redis-cli program, I was able to watch in real-time all the commands that were being sent to the server.

❯ redis-cli MONITOR
1614720201.775951 [0] "exists" "session:abc123"
1614720201.776312 [0] "get" "app:development:session:abc123"
1614720202.509717 [0] "setex" "app:development:session:abc123" "2592000" "<a bunch of data>"

The return values of the MONITOR command is a direct dump of the commands the server has received. It shows the timestamp, database, and connection info along with the command and arguments. Seeing the EXISTS command requesting a key without the prefix let me know I still had work to do. I could try new approaches without stopping the redis-cli program until I saw the desired change.