zulip/docs/production/upload-backends.md

File upload backends

Zulip in production supports a couple different backends for storing files uploaded by users of the Zulip server (messages, profile pictures, organization icons, custom emoji, etc.).

The default is the LOCAL_UPLOADS_DIR backend, which just stores files on disk in the specified directory on the Zulip server. Obviously, this backend doesn't work with multiple Zulip servers and doesn't scale, but it's great for getting a Zulip server up and running quickly. You can later migrate the uploads to S3 by following the instructions here.

We also support an S3 backend, which uses the Python boto library to upload files to Amazon S3 (or an S3-compatible block storage provider supported by the boto library).

S3 backend configuration

Here, we document the process for configuring Zulip's S3 file upload backend. To enable this backend, you need to do the following:

1. In the AWS management console, create a new IAM account (aka API user) for your Zulip server, and two buckets in S3, one for uploaded files included in messages, and another for user avatars. You need two buckets because the "user avatars" bucket is generally configured as world-readable, whereas the "uploaded files" one is not.

2. Set s3_key and s3_secret_key in /etc/zulip/zulip-secrets.conf to be the S3 access and secret keys for the IAM account.

3. Set the S3_AUTH_UPLOADS_BUCKET and S3_AVATAR_BUCKET settings in /etc/zulip/settings.py to be the names of the S3 buckets you created (e.g. exampleinc-zulip-uploads).

4. Comment out the LOCAL_UPLOADS_DIR setting in /etc/zulip/settings.py (add a # at the start of the line).

5. If you are using a non-AWS block storage provider, or certain AWS regions, you may need to explicitly configure boto. For AWS, you may need to use AWS's SIGv4 signature format (because AWS has stopped supporting the older v3 format in those regions); for other providers, you may just need to set the hostname. You can do this by adding an /etc/zulip/boto.cfg containing the following:

   [s3]
   use-sigv4 = True
   # Edit to provide your bucket's AWS region or hostname here.
   host = s3.eu-central-1.amazonaws.com
   

6. You will need to configure nginx to direct requests for uploaded files to the Zulip server (which will then serve a redirect to the appropriate place in S3), rather than serving them directly.

   With Zulip 1.9.0 and newer, you can do this automatically with the following commands run as root:

   crudini --set /etc/zulip/zulip.conf application_server no_serve_uploads true
   /home/zulip/deployments/current/scripts/zulip-puppet-apply
   

   (The first line will update your /etc/zulip/zulip.conf).

   With older Zulip, you need to edit /etc/nginx/sites-available/zulip-enterprise to comment out the nginx configuration block for /user_avatars and the include /etc/nginx/zulip-include/uploads.route line and then reload the nginx service (service nginx reload).

7. Finally, restart the Zulip server so that your settings changes take effect (/home/zulip/deployments/current/scripts/restart-server).

It's simplest to just do this configuration when setting up your Zulip server for production usage. Note that if you had any existing uploading files, this process does not upload them to Amazon S3; see migration instructions below for those steps.

S3 bucket policy

The best way to do the S3 integration with Amazon is to create a new IAM user just for your Zulip server with limited permissions. For each of the two buckets, you'll want to add an S3 bucket policy entry that looks something like this:

{
    "Version": "2012-10-17",
    "Id": "Policy1468991802321",
    "Statement": [
        {
            "Sid": "",
            "Effect": "Allow",
            "Principal": {
                "AWS": "ARN_PRINCIPAL_HERE"
            },
            "Action": [
                "s3:GetObject",
                "s3:DeleteObject",
                "s3:PutObject"
            ],
            "Resource": "arn:aws:s3:::BUCKET_NAME_HERE/*"
        },
        {
            "Sid": "Stmt1468991795389",
            "Effect": "Allow",
            "Principal": {
                "AWS": "ARN_PRINCIPAL_HERE"
            },
            "Action": "s3:ListBucket",
            "Resource": "arn:aws:s3:::BUCKET_NAME_HERE"
        }
    ]
}

The avatars bucket is intended to be world-readable, so you'll also need a block like this:

{
    "Sid": "Stmt1468991795389",
    "Effect": "Allow",
    "Principal": {
        "AWS": "*"
    },
    "Action": "s3:GetObject",
    "Resource": "arn:aws:s3:::BUCKET_NAME_HERE/*"
}

The file-uploads bucket should not be world-readable. See the documentation on the Zulip security model for details on the security model for uploaded files.

Migrating from local uploads to Amazon S3 backend

As you scale your server, you might want to migrate the uploads from your local backend to Amazon S3. Follow these instructions, step by step, to do the migration.

1. First, setup the S3 backend in the settings (all the auth stuff), but leave LOCAL_UPLOADS_DIR set -- the migration tool will need that value to know where to find your uploads.
2. Run ./manage.py transfer_uploads_to_s3. This will upload all the files from the local uploads directory to Amazon S3. By default, this command runs on 6 parallel processes, since uploading is a latency-sensitive operation. You can control this parameter using the --processes option.
3. Once the transfer script completes, disable LOCAL_UPLOADS_DIR, and restart your server (continuing the last few steps of the S3 backend setup instructions).

Congratulations! Your uploaded files are now migrated to S3.

Caveat: The current version of this tool does not migrate an uploaded organization avatar or logo.