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EFS (Elastic File System)
Amazon EFS is a fully managed, shared file system for AWS. It gives you a standard NFS filesystem that many compute resources — EC2 instances, ECS/EKS containers, and Lambda functions — can mount and read/write at the same time. It grows and shrinks automatically, so there's no capacity to provision.
The Problem It Solves
Some workloads need many machines to share the same files — a fleet of web
servers serving the same content, a content-management system, a shared home
directory, or containers that all read the same models or config. A regular disk
(EBS) is attached to one instance in one Availability Zone, so it can't
do this. Object storage (S3) can be shared, but it's an API, not a
mountable filesystem — your application can't open() a file on it like a normal
path.
EFS fills that gap: a POSIX filesystem (real directories, permissions, file locking) that lives across multiple AZs and is reachable by everything in your VPC at once.
The Three Storage Choices
Picking between EBS, EFS, and S3 is a foundational AWS decision:
| EBS | EFS | S3 | |
|---|---|---|---|
| Type | Block device (a disk) | Shared POSIX filesystem | Object store (API) |
| Who can use it | One instance, one AZ | Thousands, across AZs | Anything, via API |
| Mount as a drive? | Yes (one instance) | Yes (many, concurrently) | No |
| Typical cue | "database volume" | "shared files across instances" | "objects, static assets, data lake" |
How You Reach It
EFS lives in your VPC. In each Availability Zone you create a mount target — a network interface with an IP — and clients in that AZ mount the filesystem through their local target (so traffic stays in-AZ, which is fast and avoids cross-AZ charges). A security group on the mount target controls who can connect (NFS uses port 2049).