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zulip/docs/production/ssl-certificates.md

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Installing SSL Certificates

To keep your communications secure, Zulip runs over HTTPS only. You'll need an SSL/TLS certificate.

Fortunately, since about 2017, new options can make getting and maintaining a genuine, trusted-by-browsers certificate no longer the chore (nor expense) that it used to be.

Manual install

If you already have an SSL certificate, just install (or symlink) its files into place at the following paths:

  • /etc/ssl/private/zulip.key for the private key
  • /etc/ssl/certs/zulip.combined-chain.crt for the certificate.

Your certificate file should contain not only your own certificate but its full chain, including any intermediate certificates used by your CA. See the nginx documentation for details on what this means. If you're missing part of the chain, your server may work with some browsers, but not others and not the Zulip Android app.

Testing

Just trying in a browser is not an adequate test, because some browsers ignore errors that others don't.

Two good tests include:

  • If your server is accessible from the public Internet, use the SSL Labs tester. Be sure to check for "Chain issues"; if any, your certificate file is missing intermediate certificates.

  • Alternatively, run a command like curl -SsI https://zulip.example.com (using your server's URL) from a machine that can reach your server. Make sure that on the same machine, curl -SsI https://incomplete-chain.badssl.com gives an error; curl on some machines, including Macs, will accept incomplete chains.

Certbot (recommended)

Let's Encrypt is a free, completely automated CA launched in 2016 to help make HTTPS routine for the entire Web. Zulip offers a simple automation for Certbot, a Let's Encrypt client, to get SSL certificates from Let's Encrypt and renew them automatically.

We recommend most Zulip servers use Certbot. You'll want something else if:

  • you have an existing workflow for managing SSL certificates that you prefer;
  • you need wildcard certificates (support from Let's Encrypt planned for early 2018); or
  • your Zulip server is not on the public Internet. (In this case you can still use Certbot, but it's less convenient; and you'll want to ignore Zulip's automation.)

At initial Zulip install

To enable the Certbot automation when first installing Zulip, just pass the --certbot flag when running the install script.

The --hostname and --email options are required when using --certbot. You'll need the hostname to be a real DNS name, and the Zulip server machine to be reachable by that name from the public Internet.

After Zulip is already installed

To enable the Certbot automation on an already-installed Zulip server, run the following commands:

sudo -s  # If not already root
/home/zulip/deployments/current/scripts/setup/setup-certbot --hostname=HOSTNAME --email=EMAIL

where HOSTNAME is the domain name users see in their browser when using the server (e.g., zulip.example.com), and EMAIL is a contact address for the server admins.

How it works

When the Certbot automation in Zulip is first enabled, by either method, it creates an account for the server at the Let's Encrypt CA; requests a certificate for the given hostname; proves to the CA that the server controls the website at that hostname; and is then given a certificate. (For details, refer to Let's Encrypt.)

Then it records a flag in /etc/zulip/zulip.conf saying Certbot is in use and should be auto-renewed. A cron job checks that flag, then checks if any certificates are due for renewal, and if they are (so approximately once every 60 days), repeats the process of request, prove, get a fresh certificate.

Self-signed certificate

If you aren't able to use Certbot, you can generate a self-signed SSL certificate. This isn't suitable for production use (because it's insecure, and because browsers and the Zulip apps will complain that it's insecure), but may be convenient for testing.

To generate a self-signed certificate when first installing Zulip, just pass the --self-signed-cert flag when running the install script.

To generate a self-signed certificate for an already-installed Zulip server, run the following commands:

sudo -s  # If not already root
/home/zulip/deployments/current/scripts/setup/generate-self-signed-cert HOSTNAME

where HOSTNAME is the domain name (or IP address) to use on the generated certificate.