Unit 1.29.0 Released§

We are happy to announce Unit 1.29.0! This release enhances the configuration experience when managing Unit and provides programmability within the configuration.

  • NGINX JavaScript (njs) is now built with official Unit packages, enabling JavaScript expressions within configuration values.
  • First-time users benefit from a setup script that configures Unit with a helpful welcome page.
  • A simple command-line curl(1) wrapper simplifies configuring a running instance in real time.

In addition, Unit’s isolation capabilities have been extended so that each application can run in a new or a pre-existing Linux cgroup, but this is only a sampler of even richer per-application observability. Read on for full details of these enhancements, smaller features, and bug fixes.

NGINX JavaScript Integration§

NGINX JavaScript (njs) is a server-side JavaScript runtime, optimized for ultra-fast initialization, with a virtual machine that lives and dies with each request. Originally designed for extending NGINX, the njs architecture lends itself to integration, and now it also extends Unit!

This release brings the initial integration of the NGINX JavaScript engine to Unit. Future releases will extend these capabilities to enable more elaborate uses. With Unit 1.29.0, JavaScript template literals may be used in configuration strings to execute JavaScript expressions. A simple example is to use the ternary operator to make a routing decision.

# curl --unix-socket /var/run/control.unit.sock http://localhost/config/routes
        "action": {
            "pass": "`applications/${new Date().getHours() < 12 ? 'am' : 'pm'}`"

Here, requests are passed between different applications depending on the time of day. Note that a template literal is enclosed in backticks (``), and ${} encloses the JavaScript expression. Template literals may be used wherever Unit supports variables, and multiple expressions can appear in a single template literal.

Also, this embedded JavaScript code can access various HTTP request properties:

  • Scalars: host, uri, remoteAddr
  • Objects: args, cookies, headers

Let’s use these properties to redirect clients to the HTTPS login page if there is no session cookie:

# curl --unix-socket /var/run/control.unit.sock http://localhost/config/routes/0
    "match": {
        "scheme": "http"

    "action": {
        "return": 302,
        "location": "`https://${host}${cookies['session'] === undefined ? '/login' : uri}`"

More complex logic can be implemented using the immediately invoked function expressions (IFFE) in the template literal: an entire JavaScript function can be defined, comprising multiple statements and local variables. This defines a simple key-value log format that parses a JSON Web Token (JWT) to extract the sub claim:

# curl --unix-socket /var/run/control.unit.sock http://localhost/config/access_log
    "path": "/var/log/unit/access_kv.log",
    "format": "`timestamp=${new Date().toISOString()} ip=${remoteAddr} uri=${uri} sub=${(() => { var authz = headers['Authorization']; if (authz === undefined) { return '-'; } else { var parts = authz.slice(7).split('.').slice(0,2).map(v=>Buffer.from(v, 'base64url').toString()).map(JSON.parse); return parts[1].sub; } } )()}\n`"

Embedding IFFE code in the configuration is extremely powerful, but is typically long, difficult to read, and challenging to debug. The njs command line utility can be used to help develop JavaScript expressions.

Future releases will support loading JavaScript modules into a separate storage and later using module-based functions in the configuration.

Configuration Tools§

This release introduces two new command-line tools to simplify Unit’s installation and configuration.


The setup-unit tool automates configuring the software repository prior to installing Unit. It also verifies a fresh installation by configuring and serving a “welcome” web page. This takes some of the guesswork out of the installation process for first-time users and guides them to their next steps. Installing and running Unit on a typical Linux system is now as simple as this:

$ wget && chmod +x setup-unit
# ./setup-unit repo-config
# apt install unit || yum install unit
# ./setup-unit welcome

The setup-unit tool has other useful functions you can explore by running setup-unit --help.


The unitc tool provides a command-line interface as a wrapper for curl(1) for daily configuration and management of Unit instances. It aims to minimize typing effort and shield the users from exotic curl(1) options. In most cases, you simply specify a URI within Unit’s control API, and unitc executes the corresponding curl(1) command to read or modify the appropriate configuration portion. Unit’s control socket is detected automatically, and the appropriate HTTP method is used; several extra options cover advanced configuration and remote instance management. Here is a simple unitc example that reads and updates the entire configuration:

$ unitc /config
$ cat conf.json | unitc /config

You can find these tools and their corresponding documentation in the tools/ directory of the Unit code repository at

Per-Application Cgroups§

As we worked on Unit 1.28.0, our main goal was to extend support for any kind of observability. With 1.29.0, we add another important feature to this set.


Before we dive into the new syntax, let’s distinguish the new feature from the already supported cgroup namespaces that enable different per-process views of various system facets such as filesystem mounts, networking, or hostnames. Instead, the new cgroup support for applications is based on a Linux kernel facility that puts processes together to perform tasks on the group as a whole (for example, to enforce resource limits or add hooks for observability frameworks).

There are two parts to cgroups in Linux: the core part of organizing processes into a hierarchy, and the controllers responsible for enforcing resource limits.

With Unit 1.29.0, we support the cgroup V2 API to provide the ability to place each application into its own cgroup or have multiple applications in a single cgroup. The following configuration illustrates the newly added configuration syntax:

"applications": {
    "cgroup-demo": {
        "type": "python",
        "path": "/path/to/app/dir",
        "module": "app",
        "isolation": {
            "cgroup": {
                "path": "unit/cgroup-demo"

One thing to note about cgroups is that they are set up and controlled through the cgroupfs pseudo-filesystem; you can use tools like systemd-cgls to get a tree output of the control group content.

As mentioned initially, cgroups can be used for added application transparency on Unit, giving system profiling solutions such as eBPF the ability to collect detailed metrics per each application. At this point, there is no simple out-of-the-box solution to monitor and view the metrics that can be collected from the applications in a single control group, but we are working to expand in this direction to enable natively obtaining the performance data from Unit-configured control groups.

Meanwhile, a variety of SDKs and tools can already be used to visualize the data.

New Variables§

With version 1.29.0, we also add a new variable: $request_time records the number of seconds it took Unit to process the request. The timer sets off when the request reaches a Unit listener and stops when Unit sends the response to the client. Everything in between, e. g. in-app processing time, reading static assets, or finding the correct route on Unit, adds to the timer.

Version Updates in Language Modules§

Writing an application server for a single language is always challenging. You have to stay on top of the specifications, carefully monitoring the changes in the underlying programming language. Because Unit supports seven different languages instead of just one, you can imagine the enormity of our task in this respect. However, we are not alone! A huge shout-out goes to all the community members and supporters raising our awareness of language updates and version bumps. This kind of feedback is much appreciated and very important for us to keep Unit compatible with the latest versions of all languages we support. Due to this effort, we are proud of these additions to the list of supported languages:

  • Python 3.11
  • PHP 8.2
  • Node.js 19.0
  • Rack Version 3 in Ruby
  • Java 19 (due to Ubuntu 22.10)

Can’t say that loud enough—immense thanks to all who worked with us on these enhancements!

Full Changelog§

Changes with Unit 1.29.0                                         15 Dec 2022

    *) Change: removed $uri auto-append for "share" when loading

    *) Change: prefer system crypto policy instead of hardcoding a default.

    *) Feature: njs support with the basic syntax of JS template literals.

    *) Feature: support per-application cgroups on Linux.

    *) Feature: the $request_time variable contains the request processing

    *) Feature: "prefix" option in Python applications to set WSGI
       "SCRIPT_NAME" and ASGI root-path variables.

    *) Feature: compatibility with Python 3.11.

    *) Feature: compatibility with OpenSSL 3.

    *) Feature: compatibility with PHP 8.2.

    *) Feature: compatibility with Node.js 19.0.

    *) Feature: Ruby Rack v3 support.

    *) Bugfix: fix error in connection statistics when using proxy.

    *) Bugfix: fix HTTP cookie parsing when the value contains an equals

    *) Bugfix: PHP directory URLs without a trailing '/' would give a 503
       error (fixed with a 301 re-direct).

    *) Bugfix: missing error checks in the C API.

    *) Bugfix: report the regex status in configure summary.

Platform Updates§

  • Added support for Ubuntu 22.10
  • Added support for Fedora 37