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[Luisa Rodocker]

Laravel Horizon provides a beautiful dashboard and code-driven configuration for your Laravel powered Redis queues. Horizon allows you to easily monitor key metrics of your queue system such as job throughput, runtime, and job failures.

When using Horizon, all of your queue worker configuration is stored in a single, simple configuration file. By defining your application's worker configuration in a version controlled file, you may easily scale or modify your application's queue workers when deploying your application.

After publishing Horizon's assets, its primary configuration file will be located at config/horizon.php. This configuration file allows you to configure the queue worker options for your application. Each configuration option includes a description of its purpose, so be sure to thoroughly explore this file.

After installation, the primary Horizon configuration option that you should familiarize yourself with is the environments configuration option. This configuration option is an array of environments that your application runs on and defines the worker process options for each environment. By default, this entry contains a production and local environment. However, you are free to add more environments as needed:

When you start Horizon, it will use the worker process configuration options for the environment that your application is running on. Typically, the environment is determined by the value of the APP_ENV environment variable. For example, the default local Horizon environment is configured to start three worker processes and automatically balance the number of worker processes assigned to each queue. The default production environment is configured to start a maximum of 10 worker processes and automatically balance the number of worker processes assigned to each queue.

As you can see in Horizon's default configuration file, each environment can contain one or more "supervisors". By default, the configuration file defines this supervisor as supervisor-1; however, you are free to name your supervisors whatever you want. Each supervisor is essentially responsible for "supervising" a group of worker processes and takes care of balancing worker processes across queues.

You may add additional supervisors to a given environment if you would like to define a new group of worker processes that should run in that environment. You may choose to do this if you would like to define a different balancing strategy or worker process count for a given queue used by your application.

Within Horizon's default configuration file, you will notice a defaults configuration option. This configuration option specifies the default values for your application's supervisors. The supervisor's default configuration values will be merged into the supervisor's configuration for each environment, allowing you to avoid unnecessary repetition when defining your supervisors.

Unlike Laravel's default queue system, Horizon allows you to choose from three worker balancing strategies: simple, auto, and false. The simple strategy splits incoming jobs evenly between worker processes:

The auto strategy, which is the configuration file's default, adjusts the number of worker processes per queue based on the current workload of the queue. For example, if your notifications queue has 1,000 pending jobs while your render queue is empty, Horizon will allocate more workers to your notifications queue until the queue is empty.

When using the auto strategy, you may define the minProcesses and maxProcesses configuration options to control the minimum number of processes per queue and the maximum number of worker processes in total Horizon should scale up and down to:

The autoScalingStrategy configuration value determines if Horizon will assign more worker processes to queues based on the total amount of time it will take to clear the queue (time strategy) or by the total number of jobs on the queue (size strategy).

The balanceMaxShift and balanceCooldown configuration values determine how quickly Horizon will scale to meet worker demand. In the example above, a maximum of one new process will be created or destroyed every three seconds. You are free to tweak these values as necessary based on your application's needs.

The Horizon dashboard may be accessed via the /horizon route. By default, you will only be able to access this dashboard in the local environment. However, within your app/Providers/HorizonServiceProvider.php file, there is an authorization gate definition. This authorization gate controls access to Horizon in non-local environments. You are free to modify this gate as needed to restrict access to your Horizon installation:

Remember that Laravel automatically injects the authenticated user into the gate closure. If your application is providing Horizon security via another method, such as IP restrictions, then your Horizon users may not need to "login". Therefore, you will need to change function (User $user) closure signature above to function (User $user = null) in order to force Laravel to not require authentication.

Sometimes, you may not be interested in viewing certain jobs dispatched by your application or third-party packages. Instead of these jobs taking up space in your "Completed Jobs" list, you can silence them. To get started, add the job's class name to the silenced configuration option in your application's horizon configuration file:

Alternatively, the job you wish to silence can implement the Laravel\Horizon\Contracts\Silenced interface. If a job implements this interface, it will automatically be silenced, even if it is not present in the silenced configuration array:

Once you have configured your supervisors and workers in your application's config/horizon.php configuration file, you may start Horizon using the horizon Artisan command. This single command will start all of the configured worker processes for the current environment:

When you're ready to deploy Horizon to your application's actual server, you should configure a process monitor to monitor the php artisan horizon command and restart it if it exits unexpectedly. Don't worry, we'll discuss how to install a process monitor below.

Supervisor is a process monitor for the Linux operating system and will automatically restart your horizon process if it stops executing. To install Supervisor on Ubuntu, you may use the following command. If you are not using Ubuntu, you can likely install Supervisor using your operating system's package manager:

Supervisor configuration files are typically stored within your server's /etc/supervisor/conf.d directory. Within this directory, you may create any number of configuration files that instruct supervisor how your processes should be monitored. For example, let's create a horizon.conf file that starts and monitors a horizon process:

When defining your Supervisor configuration, you should ensure that the value of stopwaitsecs is greater than the number of seconds consumed by your longest running job. Otherwise, Supervisor may kill the job before it is finished processing.

If this job is queued with an App\Models\Video instance that has an id attribute of 1, it will automatically receive the tag App\Models\Video:1. This is because Horizon will search the job's properties for any Eloquent models. If Eloquent models are found, Horizon will intelligently tag the job using the model's class name and primary key:

If you would like to be notified when one of your queues has a long wait time, you may use the Horizon::routeMailNotificationsTo, Horizon::routeSlackNotificationsTo, and Horizon::routeSmsNotificationsTo methods. You may call these methods from the boot method of your application's App\Providers\HorizonServiceProvider:

You may configure how many seconds are considered a "long wait" within your application's config/horizon.php configuration file. The waits configuration option within this file allows you to control the long wait threshold for each connection / queue combination. Any undefined connection / queue combinations will default to a long wait threshold of 60 seconds:

Horizon includes a metrics dashboard which provides information regarding your job and queue wait times and throughput. In order to populate this dashboard, you should configure Horizon's snapshot Artisan command to run every five minutes in your application's routes/console.php file:

The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whether it intersects the relevant body's surface or not.

The true horizon is a theoretical line, which can only be observed to any degree of accuracy when it lies along a relatively smooth surface such as that of Earth's oceans. At many locations, this line is obscured by terrain, and on Earth it can also be obscured by life forms such as trees and/or human constructs such as buildings. The resulting intersection of such obstructions with the sky is called the visible horizon. On Earth, when looking at a sea from a shore, the part of the sea closest to the horizon is called the offing.[1]

The true horizon surrounds the observer and it is typically assumed to be a circle, drawn on the surface of a perfectly spherical model of the relevant celestial body, i.e., a small circle of the local osculating sphere. With respect to Earth, the center of the true horizon is below the observer and below sea level. Its radius or horizontal distance from the observer varies slightly from day to day due to atmospheric refraction, which is greatly affected by weather conditions. Also, the higher the observer's eyes are from sea level, the farther away the horizon is from the observer. For instance, in standard atmospheric conditions, for an observer with eye level above sea level by 1.70 metres (5 ft 7 in), the horizon is at a distance of about 4.7 kilometres (2.9 mi).[2]When observed from very high standpoints, such as a space station, the horizon is much farther away and it encompasses a much larger area of Earth's surface. In this case, the horizon would no longer be a perfect circle, not even a plane curve such as an ellipse, especially when the observer is above the equator, as the Earth's surface can be better modeled as an oblate ellipsoid than as a sphere.

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