If EBS volume is AZ specific, then how can we use the same volume in different AZ to make fault tolerent?

EBS volumes are indeed AZ-specific. They reside and are replicated within a single Availability Zone (AZ) for redundancy within that zone. However, there are ways to achieve fault tolerance across AZs with EBS volumes:

1. EBS Snapshots: While EBS volumes are AZ-specific, you can create snapshots of them. These snapshots are backups stored redundantly across multiple AZs within the same region. You can then use these snapshots to create new EBS volumes in different AZs. If your primary EBS volume in one AZ fails, you can launch a new instance in another AZ with a restored volume from the snapshot, achieving redundancy.
2. Amazon Elastic File System (EFS): If your use case demands frequent access to the same storage from multiple instances across AZs, consider EFS. EFS is a managed file system that automatically replicates data across AZs, providing built-in redundancy and scalability.
3. Multi-AZ Architectures: Design your architecture to leverage multiple AZs. Launch your instances in different AZs and utilize other AWS services like Route 53 for automatic failover. If an AZ experiences an outage, your application can failover to the instances in the healthy AZ using the replicated EBS snapshots or EFS.