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Object storage Serving user-uploaded files in Mastodon using external object storage
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User-uploaded files can be stored on the main server's file system, or using an external object storage server, which can be required for scaling.

Using the filesystem

The simplest way to store user uploads is by using the server's file system. This is how it works by default and is suitable for small servers.

By default, Mastodon will store file uploads under public/system in its installation directory, but that can be overridden using the PAPERCLIP_ROOT_PATH environment variable.

By default, the files are served at https://your-domain/system, which can be overridden using PAPERCLIP_ROOT_URL and CDN_HOST.

{{< hint style="info" >}} While using the server's file system is perfectly serviceable for small servers, using external object storage is more scalable. {{</ hint >}}

{{< hint style="danger" >}} The web server must be configured to serve those files but not allow listing them (that is, https://your-domain/system/ should not return a file list). This should be the case if you use the configuration files distributed with Mastodon, but it is worth double-checking. {{</ hint >}}

S3-compatible object storage backends

Mastodon can use S3-compatible object storage backends. ACL support is recommended as it allows Mastodon to quickly make the content of temporarily suspended users unavailable, or marginally improve the security of private data.

Mastodon uses the S3 API (S3_REGION, S3_ENDPOINT, S3_BUCKET, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, S3_SIGNATURE_VERSION, S3_OVERRIDE_PATH_STYLE) for all write, delete, and permissions-modification operations. This includes media uploads (from the web interface, from Mastodon API clients, and from ActivityPub servers), media deletion (when a post is edited or deleted), and blocking access to media (when an account is suspended).

Mastodon sends URLs to the web interface, Mastodon API clients, and ActivityPub servers for all 'read' operations. As a result those operations are anonymous (no authentication or authorization needed) and use plain HTTP GET methods, which means they can be routed through reverse proxies and CDNs, and can be cached. It also means that those URLs can contain host/domain names which are entirely different from those used by the S3 storage provider itself, if desired. See the detailed documentation below which describes how those URLs are constructed and which environment variables are involved.

To enable S3 storage, set the S3_ENABLED environment variable to true.

Environment variables for S3 API access

  • S3_REGION (defaults to 'us-east-1', required if using AWS S3, may not be required with other storage providers)
  • S3_ENDPOINT (defaults to 's3.<S3_REGION>.amazonaws.com', required if not using AWS S3)
  • S3_BUCKET=mastodata (replacing mastodata with the name of your bucket)
  • AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY need to be set to your credentials
  • S3_SIGNATURE_VERSION (defaults to 'v4', should be compatible with most storage providers)
  • S3_OVERRIDE_PATH_STYLE (only used if S3_ENDPOINT is configured, set this to true if the storage provider requires API operations to be sent to '<S3_BUCKET>.<S3_ENDPOINT>` (domain-style))

Environment variables for client access to media objects

  • S3_PROTOCOL (defaults to https)
  • S3_HOSTNAME (defaults to 's3-<S3_REGION>.amazonaws.com', required if not using AWS S3 and S3_ALIAS_HOST is not set)
  • S3_ALIAS_HOST (can be used instead of S3_HOSTNAME if you do not want S3_BUCKET to be included in the media URLs, and requires that you have provisioned a reverse proxy or CDN in front of the storage provider)

As noted above, Mastodon will send URLs to clients when they need to access media objects from the storage provider. The URLs are constructed as follows:

  • If S3_ALIAS_HOST is not set, then the URL will be '<S3_PROTOCOL>://<S3_HOSTNAME>/<S3_BUCKET>/<object path>'

  • If S3_ALIAS_HOST is set, then the URL will be '<S3_PROTOCOL>://<S3_ALIAS_HOST>/<object path>'

It is important to note that when S3_ALIAS_HOST is set, the bucket name is not included in the generated URL; this means the bucket name must be included in S3_ALIAS_HOST (referred to as 'domain-style' object access), or that S3_ALIAS_HOST must point to a reverse proxy or CDN which can include the bucket name in the URL it uses to send the request onward to the storage provider. This type of configuration allows you to 'hide' the usage of the storage provider from the instance's clients, which means you can change storage providers without changing the resulting URLs.

In addition to hiding the usage of the storage provider, this can also allow you to cache the media after retrieval from the storage provider, reducing egress bandwidth costs from the storage provider. This can be done in your own reverse proxy, or by using a CDN.

{{< page-ref page="admin/optional/object-storage-proxy.md" >}}

{{< hint style="info" >}} You must serve the files with CORS headers, otherwise some functions of Mastodon's web UI will not work. For example, Access-Control-Allow-Origin: * {{</ hint >}}

Optional environment variables

S3_OPEN_TIMEOUT

Default: 5 (seconds)

The number of seconds before the HTTP handler should timeout while trying to open a new HTTP session.

S3_READ_TIMEOUT

Default: 5 (seconds)

The number of seconds before the HTTP handler should timeout while waiting for an HTTP response.

S3_FORCE_SINGLE_REQUEST

Default: false

Set this to true if you run into trouble processing large files.

S3_ENABLE_CHECKSUM_MODE

Default: false

Enables verification of object checksums when Mastodon is retrieving an object from the storage provider. This feature is available in AWS S3 but may not be available in other S3-compatible implementations.

S3_STORAGE_CLASS

Default: none

When using AWS S3, this variable can be set to one of the storage class options which influence the storage selected for uploaded objects (and thus their access times and costs). If no storage class is specified then AWS S3 will use the STANDARD class, but options include REDUCED_REDUNDANCY, GLACIER, and others.

S3_MULTIPART_THRESHOLD

Default: 15 (megabytes)

Objects of this size and smaller will be uploaded in a single operation, but larger objects will be uploaded using the multipart chunking mechanism, which can improve transfer speeds and reliability.

S3_PERMISSION

Default: public-read

Defines the S3 object ACL when uploading new files. Use caution when using S3 Block Public Access and turning on the BlockPublicAcls option, as uploading objects with ACL public-read will fail (403). In that case, set S3_PERMISSION to private.

{{< hint style="danger" >}} Regardless of the ACL configuration, your S3 bucket must be set up to ensure that all objects are publicly readable but not writable or listable. At the same time, Mastodon itself should have write access to the bucket. This configuration is generally consistent across all S3 providers, and common ones are highlighted below. {{</ hint >}}

S3_BATCH_DELETE_LIMIT

Default: 1000

The official Amazon S3 API can handle deleting 1,000 objects in one batch job, but some providers may have issues handling this many in one request, or offer lower limits.

S3_BATCH_DELETE_RETRY

Default: 3

During batch delete operations, S3 providers may perodically fail or timeout while processing deletion requests. Mastodon will back off and retry the request up to this maximum number of times.

MinIO

MinIO is an open-source implementation of an S3 object provider. This section does not cover how to install it, but how to configure a bucket for use in Mastodon.

You need to set a policy for anonymous access that allows read-only access to objects contained by the bucket without allowing listing them.

To do this, you need to set a custom policy (replace mastodata with the actual name of your S3 bucket):

{
   "Version": "2012-10-17",
   "Statement": [
      {
         "Effect": "Allow",
         "Principal": {
           "AWS": "*"
         },
         "Action": "s3:GetObject",
         "Resource": "arn:aws:s3:::mastodata/*"
      }
   ]
}

Mastodon itself needs to be able to write to the bucket, so either use your admin MinIO account (discouraged) or an account specific to Mastodon (recommended) with the following policy attached (replace mastodata with the actual name of your S3 bucket):

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": "arn:aws:s3:::mastodata/*"
        }
    ]
}

You can set those policies from the MinIO Console (web-based user interface) or the command-line client (mcli / mc).

Using the MinIO Console

Connect to the MinIO Console web interface and create a new bucket (or navigate to your existing bucket):

Then, configure the “Access Policy” to a custom one that allows read access (s3:GetObject) without write access or the ability to list objects (see above):

{{< hint style="info" >}} If the MinIO Console does not allow you to set a “Custom” policy, you will likely need to update MinIO. If you are using MinIO in standalone or filesystem mode, RELEASE.2022-10-24T18-35-07Z should be a safe version to update to that does not require an involved migration procedure. {{< /hint >}}

Create a new mastodon-readwrite policy (see above):

Finally, create a new mastodon user with the mastodon-readwrite policy:

Using the command-line utility

The same can be achieved using the MinIO Client command-line utility (which can be called mc or mcli depending on where it is installed from).

Create a new bucket: mc mb myminio/mastodata

Save the anonymous access policy from above as anonymous-readonly-policy.json and the Mastodon user access policy as mastodon-readwrite.json (make sure to replace mastodata with the name of your newly-created bucket).

Set the anonymous access policy for your bucket: mc anonymous set-json anonymous-readonly-policy.json myminio/mastodata

Add a mastodon-readwrite policy: mc admin policy add myminio mastodon-readwrite mastodon-readwrite.json

Add the mastodon user (replace the password): mc admin user add myminio mastodon SECRET_PASSWORD

Apply the mastodon-readwrite policy to the mastodon user: mc admin policy set myminio mastodon-readwrite user=mastodon

Wasabi Object Storage

Create a new bucket and define its policy to allow objects to be anonymously readable but not listable:

{
   "Version": "2012-10-17",
   "Statement": [
      {
         "Effect": "Allow",
         "Principal": {
           "AWS": "*"
         },
         "Action": "s3:GetObject",
         "Resource": "arn:aws:s3:::mastodata/*"
      }
   ]
}

{{< hint style="info" >}} If you are using an old bucket, ensure you are not giving “Everyone” read access to objects through Wasabi's legacy Access Control settings, as that allows listing objects and take precedence over the IAM policy defined above.

{{< /hint >}}

Then, create a mastodon-readwrite policy to grant read and write access to your bucket:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": "arn:aws:s3:::mastodata/*"
        }
    ]
}

Finally, create a new mastodon user and don't forget to enable the mastodon-readwrite policy:

On Mastodon's side, you need to set S3_FORCE_SINGLE_REQUEST=true to properly handle large uploads.

DigitalOcean Spaces

In your DigitalOcean Spaces Bucket, make sure that “File Listing” is “Restricted” to users with access keys.

Scaleway

If you want to use Scaleway Object Storage, we strongly recommend you create a Scaleway project dedicated to your Mastodon instance assets and use a custom IAM policy.

First, create a new Scaleway project, in which you create your object storage bucket. You need to set your bucket visibility to "Private" to not allow objects to be listed.

Now that your bucket is created, you need to create API keys to be used in your Mastodon instance configuration.

Head to the IAM settings (in your organization menu, top right of the screen), and create a new IAM policy (eg mastodon-media-access)

This policy needs to have one rule, allowing it to read, write and delete objects in the Scaleway project you created above (the scope).

Then head to the IAM Applications page, and create a new one (eg my-mastodon-instance) and select the policy you created above.

Finally, click on the application you just created, then "API Keys", and create a new API key to use in your instance configuration. You should use the "Yes, set up preferred Project" option and select the project you created above as the default project for this key.

Copy the Access Key ID and Secret, and use them for your AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY Mastodon config variables.

Exoscale

In Exoscale, your bucket should not have any read ACLs (Mastodon will set the ACLs on the object themselves as appropriate).

You need to create an API Key for the Mastodon app, restricted to the Object Storage (sos) service, restricted to your bucket, and with unrestricted operations.

On Mastodon's side, you need to set S3_FORCE_SINGLE_REQUEST=true to properly handle large uploads.

Cloudflare R2

Cloudflare R2 does not support ACLs, so Mastodon needs to be instructed not to try setting them. To do that, set the S3_PERMISSION environment variable to an empty string.

{{< hint style="warning" >}} Without support for ACLs, media files from temporarily-suspended users will remain accessible. {{< /hint >}}

To get credentials for use in Mastodon, select “Manage R2 API Tokens” and create a new API token with “Edit” permissions.

{{< hint style="warning" >}} This section is currently under construction. {{< /hint >}}