Amazon Elastic File System (Amazon EFS)
- AarviTex
- Feb 1
- 4 min read
Shared File Storage for Multi-AZ Applications
1. Overview
In cloud computing, servers are not permanent.They can be stopped, replaced, or scaled automatically based on demand.
Because of this behavior, storing application data directly on servers is not recommended for production workloads.
Amazon Elastic File System (Amazon EFS) is a fully managed file storage service that enables multiple Amazon EC2 instances to access shared data concurrently. Amazon EFS is designed to be highly available and accessible across multiple Availability Zones within an AWS Region.
2. Architecture Explanation
In the illustrated architecture:
The outer green boundary represents a single AWS Region
Inside the Region, there are two Availability Zones: AZ1 and AZ2
The EFS component shown at the bottom of the diagram represents a single Amazon EFS file system that is shared across Availability Zones.
The IP labels in the diagram represent the private IP addresses of the EFS mount targets used by EC2 instances for NFS connectivity.
EC2 Instances (Server1 and Server2)
Server1 is deployed in AZ1
Server2 is deployed in AZ2
Both servers run the same application workload
The servers do not store application data locally
Amazon EFS (Elastic File System)
Amazon EFS is shown as a central shared file system
It operates at the regional level
The same EFS file system is accessible from multiple Availability Zones
IP-Based Connectivity (Mount Targets)
Each Availability Zone has its own EFS mount target
The mount targets are represented by the connection points labeled as IP addresses
EC2 instances connect to the EFS file system using these AZ-specific IP addresses
This ensures low latency and high availability
How Data Access Works
Server1 and Server2 mount the same EFS file system
Any file written by Server1 is immediately available to Server2
The file system remains available even if one Availability Zone becomes unavailable
Architectural Outcome
Compute (EC2) is decoupled from storage (EFS)
The application supports multi-AZ availability
The design is suitable for Auto Scaling and production workloads
3. Key Concepts and Terminology
Amazon Elastic File System (EFS)
Amazon EFS provides shared file storage that can be mounted on multiple EC2 instances at the same time.
Definition (Exam / Interview): A fully managed, scalable file storage service that uses the NFS protocol
AWS Real-Time Scenario: Used to store shared application files such as uploads, images, and reports
Mount
Mounting is the process of making a file system accessible at a directory in the operating system.
Definition (Exam / Interview): The process of attaching a file system to a directory
AWS Real-Time Scenario: EC2 instances mount EFS at directories such as /var/www/html
Availability Zone (AZ)
An Availability Zone is an isolated data center within an AWS Region.
Definition (Exam / Interview): An isolated location designed to provide fault tolerance
AWS Real-Time Scenario: Applications are deployed across multiple AZs to improve availability
Mount Target
A mount target is an endpoint that allows resources in a specific Availability Zone to connect to an EFS file system.
Definition (Exam / Interview): A network interface that enables access to an EFS file system
AWS Real-Time Scenario: One mount target is created per AZ for EC2 access
Network File System (NFS)
NFS is a protocol that allows file access over a network.
Definition (Exam / Interview): A distributed file system protocol for network-based file access
AWS Real-Time Scenario: Linux EC2 instances access EFS using NFS version 4
Stateless Application
A stateless application does not store data on the compute instance itself.
Definition (Exam / Interview): An application that stores state externally
AWS Real-Time Scenario: Enables Auto Scaling without data dependency on individual EC2 instances
4. AWS Real-Time Scenarios
Scenario 1: Multi-AZ Web Application
A web application runs on multiple EC2 instances behind an Application Load Balancer. Users upload images and documents.
Using Amazon EFS:
All EC2 instances access the same uploaded files
Files remain available even if instances are replaced
Application remains consistent across Availability Zones
Scenario 2: Auto Scaling Workloads
Traffic increases and Auto Scaling launches new EC2 instances.
Using Amazon EFS:
New instances mount the existing file system
Application data is immediately available
No manual file synchronization is required
5. Quick Summary for Understanding (Before Interview)
Amazon EC2 instances are temporary
Application data should not be stored locally on EC2
Amazon EFS provides shared file storage
EFS supports multiple EC2 instances simultaneously
EFS is multi-AZ by default
Uses the NFS protocol
Ideal for highly available and scalable applications
6. Interview Questions and Answers
Q1. Why is storing application data directly on EC2 not recommended?
Answer:
Because EC2 instances can be terminated or replaced, resulting in data loss.
Q2. Why is Amazon EFS preferred over Amazon EBS for shared storage?
Answer:
Amazon EBS can be attached to only one EC2 instance at a time, whereas Amazon EFS supports concurrent access by multiple EC2 instances.
Q3. Is Amazon EFS limited to a single Availability Zone?
Answer:
No. Amazon EFS is a regional service designed to be accessible across multiple Availability Zones.
7. Real-Time Interview Scenarios
Scenario 1: Shared File Visibility Issue
Question: A web application runs on multiple EC2 instances, but uploaded files are not visible on all servers. How would you fix this?
Expected Answer: Store uploaded files on Amazon EFS and mount the same file system on all EC2 instances.
Scenario 2: Auto Scaling Consistency
Question: How do you ensure new EC2 instances launched by Auto Scaling have access to existing application files?
Expected Answer: By mounting the existing Amazon EFS file system during instance startup.
Scenario 3: High Availability Requirement
Question: Which AWS storage service ensures file availability even if one Availability Zone fails?
Expected Answer: Amazon EFS, because it is designed for multi-AZ access and high availability.
8. Key Takeaways
Amazon EFS provides shared file storage
Supports multi-AZ architectures
Enables Auto Scaling without data loss
Commonly used in production workloads
Final Note
Understanding Amazon EFS and this architecture provides a strong foundation for designing reliable, scalable, and production-ready AWS applications.
Comments