Upgrading or downgrading a system with near-zero downtime requires careful planning and execution. The following steps can be taken to minimize downtime:

• Implement a load balancer: The first step is to set up a load balancer that can distribute traffic to multiple instances of the system. This ensures that if one instance is taken offline, traffic is automatically routed to the remaining instances.
• Deploy changes to a staging environment: Deploying changes to a staging environment allows for thorough testing and identification of any issues before deploying to the production environment.
• Use a rolling deployment: A rolling deployment involves updating the system one instance at a time, allowing the load balancer to distribute traffic to the remaining instances. This ensures that the system remains available throughout the deployment process.
• Monitor the deployment: Monitoring the deployment allows for the identification of any issues or errors and allows for a quick resolution.
• Use automated rollback procedures: In case of any issues during the deployment, automated rollback procedures can be used to revert to the previous version of the system.
• Notify users: It is important to notify users of any planned downtime and to provide updates on the progress of the deployment.
• Conduct post-deployment testing: After the deployment is complete, conduct thorough testing to ensure that the system is functioning as expected.