Serving a Nix store via S3

Nix has built-in support for storing and fetching store paths from Amazon S3 and S3-compatible services. This uses the same binary cache mechanism that Nix usually uses to fetch prebuilt binaries from cache.nixos.org.

In this example we will use the bucket named example-nix-cache.

Anonymous Reads to your S3-compatible binary cache

If your binary cache is publicly accessible and does not require authentication, the simplest and easiest way to use Nix with your S3 compatible binary cache is to use the HTTP URL for that cache.

For AWS S3 the binary cache URL for example bucket will be exactly https://example-nix-cache.s3.amazonaws.com or s3://example-nix-cache. For S3 compatible binary caches, consult that cache's documentation.

Your bucket will need the following bucket policy:

{
    "Id": "DirectReads",
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowDirectReads",
            "Action": [
                "s3:GetObject",
                "s3:GetBucketLocation"
            ],
            "Effect": "Allow",
            "Resource": [
                "arn:aws:s3:::example-nix-cache",
                "arn:aws:s3:::example-nix-cache/*"
            ],
            "Principal": "*"
        }
    ]
}

Authenticated Reads to your S3 binary cache

For AWS S3 the binary cache URL for example bucket will be exactly s3://example-nix-cache.

Nix will use the default credential provider chain for authenticating requests to Amazon S3.

Nix supports authenticated reads from Amazon S3 and S3 compatible binary caches.

Your bucket will need a bucket policy allowing the desired users to perform the s3:GetObject and s3:GetBucketLocation action on all objects in the bucket. The anonymous policy given above can be updated to have a restricted Principal to support this.

Authenticated Writes to your S3-compatible binary cache

Nix support fully supports writing to Amazon S3 and S3 compatible buckets. The binary cache URL for our example bucket will be s3://example-nix-cache.

Nix will use the default credential provider chain for authenticating requests to Amazon S3.

Your account will need the following IAM policy to upload to the cache:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "UploadToCache",
      "Effect": "Allow",
      "Action": [
        "s3:AbortMultipartUpload",
        "s3:GetBucketLocation",
        "s3:GetObject",
        "s3:ListBucket",
        "s3:ListBucketMultipartUploads",
        "s3:ListMultipartUploadParts",
        "s3:PutObject"
      ],
      "Resource": [
        "arn:aws:s3:::example-nix-cache",
        "arn:aws:s3:::example-nix-cache/*"
      ]
    }
  ]
}

Examples

To upload with a specific credential profile for Amazon S3:

$ nix copy nixpkgs.hello \
  --to 's3://example-nix-cache?profile=cache-upload&region=eu-west-2'

To upload to an S3-compatible binary cache:

$ nix copy nixpkgs.hello --to \
  's3://example-nix-cache?profile=cache-upload&scheme=https&endpoint=minio.example.com'