Cloud bucket mounts

The modal.CloudBucketMount is a mutable volume that allows for both reading and writing files from a cloud bucket. It currently only supports AWS S3 buckets.

AWS S3 support is built on top of AWS’ mountpoint technology and inherits its limitations.

Mounting Cloudflare R2 buckets

CloudBucketMount enables Cloudflare R2 buckets to be mounted as file system volumes. Because Cloudflare R2 is S3-Compatible the setup is very similar between R2 and S3. See modal.CloudBucketMount for usage instructions.

When creating the R2 API token for use with the mount, you need to have the ability to read, write, and list objects in the specific buckets you will mount. You do not need admin permissions, and you should not use “Client IP Address Filtering”.

Mounting S3 buckets

CloudBucketMount enables S3 buckets to be mounted as file system volumes. To interact with a bucket, you must have the appropriate IAM permissions configured (refer to the section on IAM Permissions).

import modal
import subprocess

app = modal.App()  # Note: prior to April 2024, "app" was called "stub"

s3_bucket_name = "s3-bucket-name"  # Bucket name not ARN.
s3_access_credentials = modal.Secret.from_dict({
    "AWS_ACCESS_KEY_ID": "...",
    "AWS_SECRET_ACCESS_KEY": "...",
})

@app.function(
    volumes={
        "/my-mount": modal.CloudBucketMount(s3_bucket_name, secret=s3_access_credentials)
    }
)
def f():
    subprocess.run(["ls", "/my-mount"])

To mount a bucket in read-only mode, set read_only=True as an argument.

import modal
import subprocess

app = modal.App()  # Note: prior to April 2024, "app" was called "stub"

s3_bucket_name = "s3-bucket-name"  # Bucket name not ARN.
s3_access_credentials = modal.Secret.from_dict({
    "AWS_ACCESS_KEY_ID": "...",
    "AWS_SECRET_ACCESS_KEY": "...",
})

@app.function(
    volumes={
        "/my-mount": modal.CloudBucketMount(s3_bucket_name, secret=s3_access_credentials, read_only=True)
    }
)
def f():
    subprocess.run(["ls", "/my-mount"])

While S3 mounts supports both write and read operations, they are optimized for reading large files sequentially. Certain file operations, such as renaming files, are not supported. For a comprehensive list of supported operations, consult the Mountpoint documentation.

IAM permissions

To utilize CloudBucketMount for reading and writing files from S3 buckets, your IAM policy must include permissions for s3:PutObject, s3:AbortMultipartUpload, and s3:DeleteObject. These permissions are not required for mounts configured with read_only=True.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "ModalBucketAccess",
      "Effect": "Allow",
      "Action": ["s3:ListBucket"],
      "Resource": ["arn:aws:s3:::<MY-S3-BUCKET>"]
    },
    {
      "Sid": "ModalBucketAccess",
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:PutObject",
        "s3:AbortMultipartUpload",
        "s3:DeleteObject"
      ],
      "Resource": ["arn:aws:s3:::<MY-S3-BUCKET>/*"]
    }
  ]
}