How can I implement a rolling deployment strategy for a Dockerized Python application to gradually update instances and maintain application availability?

Implementing a rolling deployment strategy involves updating instances of your Dockerized Python application one at a time, ensuring continuous availability. To achieve this, you can employ container orchestration tools like Kubernetes or Docker Swarm. So, do the steps below:

1. You should first create duplicate instances of your app with the updated code.
2. Then, gradually route traffic to the new instances while monitoring their health and performance.
3. Implement a rollback mechanism to revert to previous versions in case issues arise.
4. Last but not least, remember to use load balancers to distribute traffic intelligently between new and old instances.