Cloud bucket mounts

The modal.CloudBucketMount is a mutable volume that allows for both reading and writing files from a cloud bucket. It supports AWS S3, Cloudflare R2, and Google Cloud Storage buckets.

Cloud bucket mounts are 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 Google Cloud Storage buckets

CloudBucketMount enables Google Cloud Storage (GCS) buckets to be mounted as file system volumes. See modal.CloudBucketMount for GCS setup instructions.

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()

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": "...",
    "AWS_REGION": "..."
})

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

Specifying S3 bucket region

Amazon S3 buckets are associated with a single AWS Region. Mountpoint attempts to automatically detect the region for your S3 bucket at startup time and directs all S3 requests to that region. However, in certain scenarios, like if your container is running on an AWS worker in a certain region, while your bucket is in a different region, this automatic detection may fail.

To avoid this issue, you can specify the region of your S3 bucket by adding an AWS_REGION key to your Modal secrets, as in the code example above.

Using AWS temporary security credentials

CloudBucketMounts also support AWS temporary security credentials by passing the additional environment variable AWS_SESSION_TOKEN. Temporary credentials will expire and will not get renewed automatically. You will need to update the corresponding Modal Secret in order to prevent failures.

You can get temporary credentials with the AWS CLI with:

$ aws configure export-credentials --format env
export AWS_ACCESS_KEY_ID=XXX
export AWS_SECRET_ACCESS_KEY=XXX
export AWS_SESSION_TOKEN=XXX...

All these values are required.

Mounting a path within a bucket

To mount only the files under a specific subdirectory, you can specify a path prefix using key_prefix. Since this prefix specifies a directory, it must end in a /. The entire bucket is mounted when no prefix is supplied.

import modal
import subprocess

app = modal.App()

s3_bucket_name = "s3-bucket-name"
prefix = 'path/to/dir/'

s3_access_credentials = modal.Secret.from_dict({
    "AWS_ACCESS_KEY_ID": "...",
    "AWS_SECRET_ACCESS_KEY": "...",
})

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

This will only mount the files in the bucket s3-bucket-name that are prefixed by path/to/dir/.

Read-only mode

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

import modal
import subprocess

app = modal.App()

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>/*"]
    }
  ]
}