# Requirements and scalability

To run a Zulip server, you will need:

- A dedicated machine or VM
- A supported OS:
  - Ubuntu 20.04
  - Ubuntu 22.04
  - Debian 11
- At least 2 GB RAM, and 10 GB disk space
  - If you expect 100+ users: 4 GB RAM, and 2 CPUs
  - If you intend to [upgrade from Git][upgrade-from-git]: 3 GB RAM, or
    2G and at least 1G of swap configured.
- A hostname in DNS
- Credentials for sending email

For details on each of these requirements, see below.

[upgrade-from-git]: upgrade-or-modify.md#upgrading-from-a-git-repository

## Server

#### General

The installer expects Zulip to be the **only thing** running on the
system; it will install system packages with `apt` (like nginx,
PostgreSQL, and Redis) and configure them for its own use. We strongly
recommend using either a fresh machine instance in a cloud provider, a
fresh VM, [our Docker image][docker-zulip-homepage], or a dedicated
machine. If you decide to disregard our advice and use a server that
hosts other services, we can't support you, but [we do have some notes
on issues you'll encounter](install-existing-server.md).

#### Operating system

Ubuntu 20.04, Ubuntu 22.04, and Debian 11
are supported for running Zulip in production. You can also
run Zulip on other platforms that support Docker using
[docker-zulip][docker-zulip-homepage].

We recommend installing on the newest supported OS release you're
comfortable with, to save a bit of future work [upgrading the
operating system][upgrade-os].

If you're using Ubuntu, the
[Ubuntu universe repository][ubuntu-repositories] must be
[enabled][enable-universe], which is usually just:

```bash
sudo add-apt-repository universe
sudo apt update
```

[docker-zulip-homepage]: https://github.com/zulip/docker-zulip#readme
[upgrade-os]: upgrade-or-modify.md#upgrading-the-operating-system
[ubuntu-repositories]: https://help.ubuntu.com/community/Repositories/Ubuntu
[enable-universe]: https://help.ubuntu.com/community/Repositories/CommandLine#Adding_the_Universe_and_Multiverse_Repositories

#### Hardware specifications

- CPU and memory: For installations with 100+ users you'll need a
  minimum of **2 CPUs** and **4 GB RAM**. For installations with fewer
  users, 1 CPU and 2 GB RAM is sufficient. We strongly recommend against
  installing with less than 2 GB of RAM, as you will likely experience
  out of memory issues installing dependencies. We recommend against
  using highly CPU-limited servers like the AWS `t2` style instances
  for organizations with hundreds of users (active or no).

- Disk space: You'll need at least 10 GB of free disk space for a
  server with dozens of users. We recommend using an SSD and avoiding
  cloud storage backends that limit the IOPS per second, since the
  disk is primarily used for the Zulip database.

See our [documentation on scalability](#scalability) below for advice
on hardware requirements for larger organizations.

#### Network and security specifications

- Incoming HTTPS access (usually port 443, though this is
  [configurable](deployment.md#using-an-alternate-port))
  from the networks where your users are (usually, the public
  Internet).
- Incoming port 80 access (optional). Zulip only serves content over
  HTTPS, and will redirect HTTP requests to HTTPS.
- Incoming port 25 if you plan to enable Zulip's [incoming email
  integration](email-gateway.md).
- Incoming port 4369 should be protected by a firewall to prevent
  exposing `epmd`, an Erlang service which does not support binding
  only to localhost. Leaving this exposed will allow unauthenticated
  remote users to determine that the server is running RabbitMQ, and
  on which port, though no further information is leaked.
- Outgoing HTTP(S) access (ports 80 and 443) to the public Internet so
  that Zulip can properly manage image and website previews and mobile
  push notifications. Outgoing Internet access is not required if you
  [disable those
  features](https://zulip.com/help/allow-image-link-previews).
- Outgoing SMTP access (usually port 587) to your [SMTP
  server](email.md) so that Zulip can send emails.
- A domain name (e.g. `zulip.example.com`) that your users will use to
  access the Zulip server. In order to generate valid SSL
  certificates [with Certbot][doc-certbot], and to enable other
  services such as Google authentication, public DNS name is simpler,
  but Zulip can be configured to use a non-public domain or even an IP
  address as its external hostname (though we don't recommend that
  configuration).
- Zulip supports [running behind a reverse proxy][reverse-proxy].
- Zulip configures [Smokescreen, an outgoing HTTP
  proxy][smokescreen-proxy], to protect against [SSRF attacks][ssrf],
  which prevents user from making the Zulip server make requests to
  private resources. If your network has its own outgoing HTTP proxy,
  Zulip supports using that instead.

[ssrf]: https://owasp.org/www-community/attacks/Server_Side_Request_Forgery
[smokescreen-proxy]: deployment.md#customizing-the-outgoing-http-proxy
[reverse-proxy]: deployment.md#putting-the-zulip-application-behind-a-reverse-proxy
[email-mirror-code]: https://github.com/zulip/zulip/blob/main/zerver/management/commands/email_mirror.py

## Credentials needed

#### SSL certificate

Your Zulip server will need an SSL certificate for the domain name it
uses. For most Zulip servers, the recommended (and simplest) way to
get this is to just [use the `--certbot` option][doc-certbot] in the
Zulip installer, which will automatically get a certificate for you
and keep it renewed.

For test installations, an even simpler alternative is always
available: [the `--self-signed-cert` option][doc-self-signed] in the
installer.

If you'd rather acquire an SSL certificate another way, see our [SSL
certificate documentation](ssl-certificates.md).

[doc-certbot]: ssl-certificates.md#certbot-recommended
[doc-self-signed]: ssl-certificates.md#self-signed-certificate

#### Outgoing email

- Outgoing email (SMTP) credentials that Zulip can use to send
  outgoing emails to users (e.g. email address confirmation emails
  during the signup process, message notification emails, password
  reset, etc.). If you don't have an existing outgoing SMTP solution,
  read about
  [free outgoing SMTP options and options for prototyping](email.md#free-outgoing-email-services).

Once you have met these requirements, see [full instructions for installing
Zulip in production](install.md).

[trusty-eol]: https://wiki.ubuntu.com/Releases

## Scalability

This section details some basic guidelines for running a Zulip server
for larger organizations (especially >1000 users or 500+ daily active
users). Zulip's resource needs depend mainly on 3 parameters:

- daily active users (e.g. number of employees if everyone's an
  employee)
- total user accounts (can be much larger)
- message volume.

In the following, we discuss a configuration with at most two types of
servers: application servers (running Django, Tornado, RabbitMQ,
Redis, Memcached, etc.) and database servers. Of the application
server services, Django dominates the resource requirements. One can
run every service on its own system (as
[docker-zulip](https://github.com/zulip/docker-zulip) does) but for
most use cases, there's little scalability benefit to doing so. See
[deployment options](deployment.md) for details on
installing Zulip with a dedicated database server.

- **Dedicated database**. For installations with hundreds of daily
  active users, we recommend using a [remote PostgreSQL
  database](postgresql.md), but it's not required.

- **RAM:** We recommended more RAM for larger installations:

  - With 25+ daily active users, 4 GB of RAM.
  - With 100+ daily active users, 8 GB of RAM.
  - With 400+ daily active users, 16 GB of RAM for the Zulip
    application server, plus 16 GB for the database.
  - With 2000+ daily active users 32 GB of RAM, plus 32 GB for the
    database.
  - Roughly linear scaling beyond that.

- **CPU:** The Zulip application server's CPU usage is heavily
  optimized due to extensive work on optimizing the performance of
  requests for latency reasons. Because most servers with sufficient
  RAM have sufficient CPU resources, CPU requirements are rarely an
  issue. For larger installations with a dedicated database, we
  recommend high-CPU instances for the application server and a
  database-optimized (usually low CPU, high memory) instance for the
  database.

- **Disk for application server:** We recommend using [the S3 file
  uploads backend][s3-uploads] to store uploaded files at scale. With
  the S3 backend configuration, we recommend 50 GB of disk for the OS,
  Zulip software, logs and scratch/free space. Disk needs when
  storing uploads locally

- **Disk for database:** SSD disk is highly recommended. For
  installations where most messages have <100 recipients, 10 GB per 1M
  messages of history is sufficient plus 1 GB per 1000 users is
  sufficient. If most messages are to public streams with 10K+ users
  subscribed (like on chat.zulip.org), add 20 GB per (1000 user
  accounts) per (1M messages to public streams).

- **Example:** When
  [the Zulip development community](https://zulip.com/development-community/) server
  had 12K user accounts (~300 daily actives) and 800K messages of
  history (400K to public streams), it was a default configuration
  single-server installation with 16 GB of RAM, 4 cores (essentially
  always idle), and its database was using about 100 GB of disk.

- **Disaster recovery:** One can easily run a warm spare application
  server and a warm spare database (using [PostgreSQL warm standby
  replicas][streaming-replication]). Make sure the warm spare
  application server has copies of `/etc/zulip` and you're either
  syncing `LOCAL_UPLOADS_DIR` or using the [S3 file uploads
  backend][s3-uploads].

- **Sharding:** Zulip releases do not fully support dividing Tornado
  traffic for a single Zulip realm/organization between multiple
  application servers, which is why we recommend a hot spare over
  load-balancing. We don't have an easily deployed configuration for
  load-balancing Tornado within a single organization, and as a result
  can't currently offer this model outside of enterprise support
  contracts.

  - Zulip 2.0 and later supports running multiple Tornado servers
    sharded by realm/organization, which is how we scale Zulip Cloud.
    [Contact us][contact-support] for help implementing the sharding policy.

Scalability is an area of active development, so if you're unsure
whether Zulip is a fit for your organization or need further advice
[contact Zulip support][contact-support].

For readers interested in technical details around what features
impact Zulip's scalability, this [performance and scalability design
document](../subsystems/performance.md) may also be of interest.

[s3-uploads]: upload-backends.md#s3-backend-configuration
[streaming-replication]: deployment.md#postgresql-warm-standby
[contact-support]: https://zulip.com/help/contact-support
