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Laravel Drivers for Redis Sentinel

Redis Sentinel integration for Laravel and Lumen.

Redis Sentinel facilitates high-availability, monitoring, and load-balancing for Redis servers configured for master-slave replication. Laravel includes built-in support for Redis, but we cannot configure Sentinel setups flexibly out-of-the-box. This limits configuration of Sentinel to a single service.

For instance, if we wish to use Redis behind Sentinel for both the cache and session in Laravel's API, we cannot set separate Redis databases for for both types of data like we can in a standard, single-server Redis setup without Sentinel. This causes issues when we need to clear the cache, because Laravel erases stored session information as well.

This package wraps the configuration of Laravel's broadcasting, cache, session, and queue APIs for Sentinel with the ability to set options for our Redis services independently. It adds Sentinel support for Laravel Horizon and fixes other compatibility issues.

We configure the package separately from Laravel's standard Redis configuration so we can choose to use the Sentinel connections as needed by the environment. A developer may use a standalone Redis server in their local environment, while production environments operate a Redis Sentinel set of servers.

Contents

• Quickstart (TL;DR)
• Requirements
• Installation
• Configuration Options
  • Environment-Based Configuration
  • Standard Laravel Configuration Files
  • Package Configuration File
  • Hybrid Configuration
• Override the Standard Redis API
• Executing Redis Commands (RedisSentinel Facade)
  • Dependency Injection
• Other Sentinel Considerations
• Laravel Horizon
• Testing
• License
• Appendix: Environment Variables
• Appendix: Configuration Examples

Requirements

• PHP 5.4 or greater
• Redis 2.8 or greater (for Sentinel support)
• Predis 1.1 or greater (for Sentinel client support)
• Laravel or Lumen 5.0 or greater (4.x doesn't support the required Predis version)

Note: Laravel 5.4 introduced the ability to use the PhpRedis extension as a Redis client for the framework. This package does not yet support the PhpRedis option.

This Readme assumes prior knowledge of configuring Redis for Redis Sentinel and using Redis with Laravel or Lumen.

Installation

We're using Laravel, so we'll install through Composer, of course!

For Laravel/Lumen 5.4 and above:

For Laravel/Lumen 5.3 and below:

Note: According to the Laravel release schedule, all Laravel versions prior to 5.4 exited their active development and support periods in August of 2017. After December, 2017, this package will no longer provide feature releases on the 1.x branch for Laravel versions earlier than 5.4.

If the project does not already use Redis with Laravel, this will install the Predis package as well.

Register the Service Provider

Laravel 5.5 brings package discovery! No service provider registration required in Laravel 5.5+.

To use the drivers in Laravel 5.4 and below, add the package's service provider to config/app.php:

In Lumen, register the service provider in bootstrap/app.php:

Quickstart (TL;DR)

After installing the package, set the following in .env:

The following should now use Redis Sentinel connections:

This example configures the package through the environment. It overrides Laravel's standard Redis API by setting REDIS_DRIVER to redis-sentinel. See appendix for all of the configurable environment variables. Optionally, enable the RedisSentinel facade.

For those that need a quick development Sentinel server cluster, try the start-cluster.sh script included with the package's testing files.

Configuration

We can configure the package three ways depending on the needs of the application:

• Environment-Based Configuration
• Standard Laravel Configuration Files
• Package Configuration File

A hybrid configuration uses two or more of these methods.

With the release of version 2.2.0, the package supports simple configuration through environment variables with a default configuration structure suitable for many applications. This especially relieves Lumen users of the need to create several config files that may not already exist with an initial Lumen installation.

The package continues to support advanced configuration through standard config files without requiring changes for existing projects.

Environment-Based Configuration

For suitable applications, the package's ability to configure itself from the environment eliminates the need to create or modify configuration files in many scenarios. The package automatically configures Redis Sentinel connections and the application broadcasting, cache, session, and queue services for these connections using environment variables.

Developers may still configure the package through standard Laravel configuration files when the application requirements exceed the package's automatic configuration capacity.

Typically, we assign the application environment variables in the project's .env file during development. The configuration for a basic application may be as simple as setting the following values in this file:

This sets up the default Redis Sentinel connection for the package's services that we can access through the RedisSentinel facade (or by resolving app('redis-sentinel') from the container) like we would for Laravel's standard Redis API. To use this Sentinel connection for Laravel's broadcasting, cache, session, or queue services, change the following values as well:

Connection-Specific Configuration

In many cases, we'd set different connection parameters for the application broadcasts, cache, session, and queue. We may configure different Redis databases for our cache and session (so that clearing the cache doesn't erase our user session information), and the Redis servers that contain the application queue may reside behind a different Sentinel service (master group name):

Specifying Multiple Hosts

To supply multiple hosts for a connection through environment variables, set the value of any *_HOST variable to a comma-seperated string of hostnames or IP addresses:

Hosts share the port set for the connection unless we explicitly include the port number after the hostname as shown.

Mixed Applications

The previous examples set the REDIS_HOST and REDIS_PORT variables, which Laravel also reads to configure standard Redis connections. This enables developers to use the same variables in development, with a single Redis server, and in production, with a full set of Sentinel servers. However, if an application contains code that sends requests to both Redis and Sentinel connections in the same environment, we must assign one or more of the Sentinel-specific variables instead:

Other Environment Configuration Options

We can change the value of REDIS_DRIVER to redis-sentinel to override the standard Laravel Redis API.

For a full list of the environment variables this package consumes, see the appendix. Check out the package's internal configuration file or the environment-based configuration examples to better understand how the package uses environment variables.

Using Standard Configuration Files

In addition to environment-based configuration, the package allows developers to configure Redis Sentinel integration through Laravel's standard configuration files. This option exists for cases when applications require more advanced or specialized Sentinel configuration than the package's default environment-based configuration can provide.

For this configuration method, we'll modify the following config files:

• config/database.php - to define the Redis Sentinel connections
• config/broadcasting.php - to define the Redis Sentinel broadcaster
• config/cache.php - to define a Redis Sentinel cache store
• config/session.php - to set the Redis Sentinel connection for sessions
• config/queue.php - to define a Redis Sentinel queue connection

Note: Lumen users may create a package config file instead to avoid the need to create all of the above files if they don't exist.

When environment-based configuration satisfies the needs of the application, we do not need to modify any config files. The code illustrated in the following sections overrides the package's automatic configuration.

Redis Sentinel Connection Configuration

We'll configure the Redis Sentinel database connections separately from Laravel's default Redis database connection. This enables us to use Laravel's standard Redis functionality side-by-side if needed, such as if a developer runs a single Redis server in their local environment, while the production environment operates a full set of Redis and Sentinel servers. We don't need to remove the 'redis' driver config block that ships with Laravel by default.

Note: Laravel passes these configuration options to the Predis client library, so we can include advanced configuration options here if needed. See the Predis documentation for more information.

Basic Configuration

For a simple setup with a single Sentinel server, add the following block to config/database.php for the 'redis-sentinel' database driver.

As you can see, our 'default' connection includes the address or hostname of the Sentinel server and the port that the application connects to (typically 26379). Because Sentinel doesn't support authentication directly, we'll set the password for our Redis server in the 'parameters' array, which also includes the Redis database to use for the connection. The 'service' option declares the service name of the set of Redis servers configured in Sentinel as a service.

Take note of the sub-array in the top level array for the 'default' connection. If we choose to add additional Sentinel servers to this configuration, we'll wrap the definition of each host in another array, like we can see in the following section.

Of course, be sure to add the environment configuration variables from the example above to .env.

Advanced Configuration

The configuration block above is almost a drop-in replacement for Laravel's built-in 'redis' connection configuration that we could use to configure an application for Sentinel without this package. However, we cannot configure Laravel's standard Redis connections for anything more complex than this basic Sentinel setup because of limitations in the way Laravel parses its Redis configuration. A single Sentinel server or connection is typically insufficient for highly-available or complex applications. Read the examples in the appendix for more robust configuration instructions:

• Connections with Multiple Sentinel Hosts
• Multiple Service-Specific Connections

Other Sentinel Connection Options

The Predis client supports some additional configuration options that determine how it handles connections to Sentinel servers. We can add these to the global 'options' array for all Sentinel connections or to a local 'options' array for a single connection. The default values are shown below:

Broadcasting, Cache, Session, and Queue Drivers

After configuring the Sentinel database connections, we can instruct Laravel to use these connections for the application's other redis-enabled services. Remember that we don't need to set Sentinel connections for all of these services. We could select a standard Redis connection for one and a Sentinel connection for another, if desired, but we likely want to take advantage of Sentinel for all of our Redis connections if it's available.

Note: We can omit (or remove) the following configuration blocks entirely and the package will configure these services for us. If we created custom Sentinel connections as above, we may need to declare those connection names.

Broadcasting

Add the following connection definition to config/broadcasting.php in the 'connections' array:

...and change the BROADCAST_DRIVER environment variable to redis-sentinel in .env.

If the application contains a specific connection in the 'redis-sentinel' database configuration for the event broadcasting, replace 'default' with its name.

Cache

Add the following store definition to config/cache.php in the 'stores' array:

...and change the CACHE_DRIVER environment variable to redis-sentinel in .env.

If the application contains a specific connection in the 'redis-sentinel' database configuration for the cache, replace 'default' with its name.

Session

Change the SESSION_DRIVER environment variable to redis-sentinel in .env. Then, in config/session.php, set the 'connection' directive to 'default', or the name of the specific connection created for storing sessions from the 'redis-sentinel' database configuration.

Queue

Add the following connection definition to config/queue.php in the 'connections' array:

...and change the QUEUE_CONNECTION (Laravel 5.7+) or QUEUE_DRIVER (Laravel <= 5.6) environment variable to redis-sentinel in .env.

If the application contains a specific connection in the 'redis-sentinel' database configuration for the queue, replace 'connection' => 'default' with its name.

Using a Package Configuration File

Lumen projects don't include configuration files by default. Instead, by convention, Lumen reads configuration information from the environment. If we wish to configure this package through config files as described in the previous section, rather than using the environment-based configuration, we can add a single package configuration file: config/redis-sentinel.php. This alleviates the need to create several standard config files in Lumen.

The package configuration file contains elements that the package merges back into the main configuration locations at runtime. To illustrate, when the custom redis-sentinel.php file contains:

...the package will set the database.redis-sentinel configuration value from the value of redis-sentinel.database.redis-sentinel when the application boots unless the key already exists.

We can customize the package's internal config file by copying it into our project's config/ directory and changing the values as needed. Lumen users may need to create this directory if it doesn't exist.

A custom package config file needs only to contain the top-level elements that developer wishes to customize: in the code shown above, the custom config file only overrides the package's default configuration for Redis Sentinel connections, so the package will still automatically configure the broadcasting, cache, session, and queue services using environment variables.

Hybrid Configuration

Although unnecessary in most cases, developers may combine two or more of the configuration methods provided by this package. For example, an application may contain a package config file that defines the Redis Sentinel connections, but rely on the package's automatic environment-based configuration to set up the cache, session, queue, and broadcasting services for Sentinel.

The package uses configuration data in this order of precedence:

1. Standard Laravel configuration files
2. A custom package configuration file
3. Automatic environment-based configuration

This means that package-specific values in the standard config files override values in a custom package config file, which, in turn, override the package's default automatic configuration through environment variables. In other words, a custom package config file inherits the values from the package's default configuration that it does not explicitly declare, and the main application configuration receives the values from both of these that it does not provide in a standard config file.

Override the Standard Redis API

This package adds Redis Sentinel drivers for Laravel's caching, session, and queue APIs, and the developer may select which of these to utilize Sentinel connections for. However, Laravel also provides an API for interacting with Redis directly through the Redis facade, or through the Redis connection manager which we can resolve through the application container (app('redis'), dependency injection, etc.).

When installed, this package does not impose the use of Sentinel for all Redis requests. In fact, we can choose to use Sentinel connections for some features and continue to use Laravel's standard Redis connections for others. By default, this package does not replace Laravel's built-in Redis API.

As an example, we may decide to use Sentinel connections for the application's cache and sessions, but directly interact with a single Redis server using Laravel's standard Redis connections.

That said, this package provides the option to override Laravel's Redis API so that any Redis commands use the Sentinel connection configuration defined by the 'redis-sentinel' database driver.

To use this feature, add the following configuration directive to the root of the 'redis' connection definition in config/database.php (if not using environment-based configuration):

...and add the environment variable REDIS_DRIVER to .env with the value redis-sentinel.

When enabled, Redis commands executed through the Redis facade or the redis service (app('redis'), etc) will operate using the Sentinel connections.

This makes it easier for developers to use a standalone Redis server in their local environments and switch to a full Sentinel set of servers in production.

Note: When using the package with Laravel Horizon, this change will cause Horizon to run over a Sentinel connection as well.

Executing Redis Commands (RedisSentinel Facade)

If we need to send Redis commands to Redis instances behind a Sentinel server directly, such as we can through the Redis facade, but we don't want to override Laravel's Redis API as above, we can use the RedisSentinel facade provided by this package or resolve the redis-sentinel service from the application container:

This provides support for uncommon use cases for which an application may need to connect to both standard Redis servers and Sentinel clusters in the same environment. When possible, follow the approach described in the previous section to uniformly connect to Sentinel throughout the application to decouple the code from the Redis implementation.

The facade is not auto-aliased in Laravel 5.5+ for future compatibility with the PhpRedis extension. To enable the facade in Laravel, add the following alias to the 'aliases' array in config/app.php:

In Lumen, add the alias to bootstrap/app.php:

Dependency Injection

For those that prefer to declare the Redis Sentinel manager as a dependency of a class rather than using the facade, we can type-hint the interface that the container will resolve when building an object from the container:

The above explicitly requests an instance of the package's Sentinel service. If we override the Redis API, we can use the standard Redis contract instead, and the application will inject the appropriate service based on the configuration:

Other Sentinel Considerations

The following sections describe some characteristics to keep in mind when working with Sentinel connections.

Read and Write Operations

To spread load between available resources, the client attempts to execute read operations on Redis slave servers when initializing a connection. Commands that write data will always execute on the master server.

Transactions

All commands in a transaction, even read-only commands, execute on the master Redis server. When it makes sense to do so, avoid calling read commands within a transaction to improve load-balancing.

If a transaction aborts because of a connection failure, the package attempts to reconnect and retry the transaction until it exhausts the configured number of allowed attempts (retry_limit), or until the entire transaction succeeds.

Important: Predis provides a specialized MULTI/EXEC abstraction that we can obtain by calling transaction() with no arguments. This API is not protected by Sentinel connection failure handling. For high-availability, use the Laravel API by passing a closure to transaction().

Publish/Subscribe

For PUB/SUB messaging, the client publishes messages to the master server. When subscribing, the package attempts to connect to a slave server first before falling-back to the master. Like with read operations, this helps to distribute the load away from the master because messages published to the master propagate to each of the slaves.

Applications with long-running subscribers need to extend the timeout of the connection or disable it by setting read_write_timeout to 0. Additionally, we also need to extend or disable the timeout configuration directive on the Redis servers that the application subscribes to.

When a subscriber connection fails, the package will attempt to reconnect to another server and resume listening for messages. We may want to set the value of retry_limit to -1 on connections with long-running subscribers so that the client continues to retry forever. Note that a subscriber may miss messages published to a channel while re-establishing the connection.

Important: Predis provides a PUB/SUB consumer that we can obtain by calling pubSubLoop() with no arguments. This API is not protected by Sentinel connection failure handling. For high-availability, use the Laravel API by passing a closure to subscribe() or psubscribe().

Laravel Horizon

Versions 2.4.0 and greater of this package provide for the use of Sentinel connections with the Laravel Horizon queue management tool in compatible applications (Laravel 5.5+).

After installing Horizon, we need to update some configuration settings in config/horizon.php:

If needed, change 'use' => 'default' to the name of the Sentinel connection to use for the Horizon backend as configured in config/database.php.

Important: The standard 'redis' connections array in config/database.php must contain an element with the same key as the Sentinel connection specified for the 'use' directive or Horizon throws an exception. Currently, Horizon does not provide a way for this package to handle this behavior, but an (in-progress) pull request may eliminate this requirement in the future. This element can contain any value (but a matching Redis connection config seems most appropriate).

Change the backend driver for Horizon's internal metadata to 'redis-sentinel' by adding the following element to the top-level array:

...and assign the value of redis-sentinel to HORIZON_DRIVER in .env.

Then, add an entry to the 'waits' array for any Sentinel queues:

Next, change the connection driver to redis-sentinel for each of the queue workers that should use Sentinel connections in the 'environments' block:

Horizon will now use the application's Redis Sentinel connections to monitor and process our queues.

Note: If we already configured the package to override Laravel's standard Redis API (by setting REDIS_DRIVER to redis-sentinel, for example), we don't need to change HORIZON_DRIVER to 'redis-sentinel'. The package already routes all Redis operations through Sentinel connections.

Testing

This package includes a PHPUnit test suite with unit tests for the package's classes and an integration test suite for Sentinel-specific functionality and compatibility fixes. These tests do not verify every Redis command because Predis and Laravel both contain full test suites themselves, and because the package code simply wraps these libraries.

The unit tests do not require live Redis servers. Read the next section for integration testing environment suggestions.

Note: Composer does not download this package's testing files with a normal installation. We need to clone the package repository directly or install it with the --prefer-source option.

Integration Tests

This package's integration test suite validates Sentinel- and Redis-specific functionality against real servers. These tests require at least one Sentinel server that monitors a Redis master. Additionally, at least one replica should synchronize with the master for optimal test coverage. Developers may supply their own servers or start an environment using the package's tools described below.

To customize the Sentinel connection settings used by the integration tests, copy phpunit.xml.dist to phpunit.xml and change the constants defined in the <php>...</php> block.

We can run the start-cluster.sh script provided in the project's root directory to spin up Redis and Sentinel servers for a testing environment. Read the script help page for usage information.

Docker users may wish to use the script to start testing servers in a container:

The package provides a Compose file with the same options for running tests:

Developers can also customize the Compose file by copying docker-compose.yml to docker-compose.override.yml.

License

The MIT License (MIT). Please see the LICENSE File for more information.

Appendix: Environment Variables

The package consumes the following environment variables when using the default environment-based configuration. Developers only need to supply values for the variables that apply to their particular application and Redis setup. The default values are sufficient in most cases.

REDIS_{HOST,PORT,PASSWORD,DATABASE}

The basic connection parameters used by default for all Sentinel connections.

To simplify environment configuration, this package attempts to read both the REDIS_* and the REDIS_SENTINEL_* environment variables that specify values shared by multiple Sentinel connections. If an application does not execute commands through both Redis Sentinel and standard Redis connections at the same time, this feature allows developers to use the same environment variale names in development (with a single Redis server) and in production (with a full set of Sentinel servers).

• REDIS_HOST - One or more hostnames or IP addresses. Defaults to localhost when unset.
• REDIS_PORT - The listening port of the Sentinel servers. Defaults to 26379 for Sentinel connections when unset.
• REDIS_PASSWORD - The password, if any, used to authenticate with the Redis servers behind Sentinel (Sentinels don't support password auth themselves).
• REDIS_DATABASE - The number of the database to select when issuing commands to the Redis servers behind Sentinel (0 to 15 in a normal Redis config). Defaults to 0.

REDIS_SENTINEL_{HOST,PORT,PASSWORD,DATABASE}

Set these variables instead of the above when the application uses both standard Redis and Redis Sentinel connections at the same time.

• REDIS_SENTINEL_HOST - See REDIS_HOST.
• REDIS_SENTINEL_PORT - See REDIS_PORT.
• REDIS_SENTINEL_PASSWORD - See REDIS_PASSWORD.
• REDIS_SENTINEL_DATABASE - See REDIS_DATABASE.

REDIS_SENTINEL_SERVICE

The Redis master group name (as specified in the Sentinel server configuration file) that identifies the default Sentinel service used by all Sentinel connections. Defaults to mymaster.

Set REDIS_CACHE_SERVICE, REDIS_SESSION_SERVICE, or REDIS_QUEUE_SERVICE to override this value for a service-specific connection.

REDIS_SENTINEL_{TIMEOUT,RETRY_LIMIT,RETRY_WAIT,DISCOVERY}

The Predis client supports some additional configuration options that determine how it handles connections to Sentinel servers.

• REDIS_SENTINEL_TIMEOUT - The amount of time (in seconds) the client waits before determining that a connection attempt to a Sentinel server failed. Defaults to 0.100.
• REDIS_SENTINEL_RETRY_LIMIT - The number of attempts the client tries to contact a Sentinel server before it determines that it cannot reach all Sentinel servers in a quorum. A value of 0 instructs the client to throw an exception after the first failed attempt, while a value of -1 causes the client to continue to retry connections to Sentinel indefinitely. Defaults to 20.
• REDIS_SENTINEL_RETRY_WAIT - The amount of time (in milliseconds) the client waits before attempting to contact another Sentinel server if the previous server did not respond. Defaults to 1000.
• REDIS_SENTINEL_DISCOVERY - Instructs the client to query the first reachable Sentinel server for an updated set of Sentinels each time the client needs to establish a connection with a Redis master or slave server. Defaults to false.

REDIS_DRIVER

Set the value of this variable to redis-sentinel to override Laravel's standard Redis API.

BROADCAST_DRIVER, CACHE_DRIVER, SESSION_DRIVER, QUEUE_CONNECTION

Laravel uses these to select the backends for the application broadcasting, cache, session, and queue services. Set the value to redis-sentinel for each service that the application should use Sentinel connections for.

Note: Laravel 5.7 renamed QUEUE_DRIVER to QUEUE_CONNECTION in the default configuration files.

REDIS_{BROADCAST,CACHE,SESSION,QUEUE}_{HOST,PORT,PASSWORD,DATABASE,SERVICE}

These variables configure service-specific connection parameters when they differ from the default Sentinel connection parameters for the broadcasting, cache, session, and queue connections. For example:

• REDIS_BROADCAST_HOST - Overrides REDIS_HOST or REDIS_SENTINEL_HOST for the default broadcasting connection.
• REDIS_CACHE_PORT - Overrides REDIS_PORT or REDIS_SENTINEL_PORT for the default cache connection.
• REDIS_SESSION_PASSWORD - Overrides REDIS_PASSWORD or REDIS_SENTINEL_PASSWORD for the default session connection.
• REDIS_QUEUE_DATABASE - Overrides REDIS_DATABASE or REDIS_SENTINEL_DATABASE for the default queue connection.
• REDIS_QUEUE_SERVICE - Overrides REDIS_SENTINEL_SERVICE for the default queue connection.

BROADCAST_REDIS_CONNECTION, BROADCAST_REDIS_SENTINEL_CONNECTION

The name of the Sentinel connection to select for application broadcasting when BROADCAST_DRIVER equals redis-sentinel. It defaults to the package's internal, auto-configured broadcasting connection when unset.

CACHE_REDIS_CONNECTION, CACHE_REDIS_SENTINEL_CONNECTION

The name of the Sentinel connection to select for the application cache when CACHE_DRIVER equals redis-sentinel. It defaults to the package's internal, auto-configured cache connection when unset.

QUEUE_REDIS_CONNECTION, QUEUE_REDIS_SENTINEL_CONNECTION

The name of the Sentinel connection to select for the application queue when QUEUE_CONNECTION (Laravel 5.7+) or QUEUE_DRIVER (Laravel <= 5.6) equals redis-sentinel. It defaults to the package's internal, auto-configured queue connection when unset.

SESSION_CONNECTION

The name of the Sentinel connection to select for storing application sessions when SESSION_DRIVER equals redis-sentinel. It defaults to the package's internal, auto-configured session connection when unset unless the application configuration already contains a value for session.connection.

REDIS_SENTINEL_AUTO_BOOT

When set to true, this flag instructs the package to boot the package after it registers its services without waiting for the application boot phase. This provides a way for applications that use Sentinel connections in other service providers to initialize the package immediately.

Appendix: Configuration Examples

• Environment-based Configuration Examples
  • Development vs. Production
• Configuration File Examples
  • Multi-Sentinel Configuration
  • Multi-Service Configuration

Environment-based Configuration Examples

Supplemental examples for environment-based-configuration.

Development vs. Production

This example shows how we might change the values of environment variables between environments when we run a single Redis server in development and a full set of Sentinel servers in production.

Don't forget to run the artisan config:cache command in production when possible. This dramatically improves the configuration loading time for the application and this package.

Best practice suggests that we avoid using the development .env file in production environments. Consider other means to set environment variables:

"phpdotenv is made for development environments, and generally should not be used in production. In production, the actual environment variables should be set so that there is no overhead of loading the .env file on each request. This can be achieved via an automated deployment process with tools like Vagrant, chef, or Puppet, or can be set manually with cloud hosts..."

Configuration File Examples

These examples demonstrate how to setup Laravel's standard configuration files to configure the package for more-advanced setups. For an introduction to using configuration files, read the config file documentation.

Multi-Sentinel Connection Configuration

In a true highly-available Redis setup, we'll run more than one Sentinel server in a quorum. This adds redundancy for a failure event during which one or more Sentinel servers become unresponsive. We can add multiple Sentinel server definitions to our 'default' connection in config/database.php:

With this configuration, we declare three Sentinel servers that can handle requests for our Redis service, mymaster (the master group name as specified in the Sentinel server configuration file). If one of the Sentinel servers fails, the Predis client will select a different Sentinel server to send requests to.

Typically, in a clustered environment, we don't want to hard-code each server into our configuration like above. We may install some form of load balancing or service discovery to route requests to a Sentinel server through an aggregate hostname, such as sentinels.example.com, for flexible deployment and arbritrary scaling.

Multi-service Connection Configuration

As we mentioned previously, we likely want to separate the Redis connections Laravel uses for each of our services. For instance, we'd use separate databases on a Redis server for our cache and session storage. In this example, we may also want to create a database on a different set of Redis servers managed by Sentinel for something like a feed. For this setup, we'll configure multiple 'redis-sentinel' connections:

Notice that we removed the global 'options' array and created a local 'options' array for each connection. In this example setup, we store the application cache and sessions on one Redis server set, and feed data in another set. In the first connection block, we set the Redis database for storing cache data to 0, and the database for session data to 1, which allows us to clear our application cache without erasing user sessions.

This example setup includes a second set of Redis servers for storing feed data. The example Sentinel servers contain configuration for the first set with the service name, mymaster, and for the secord set with the service name, feed-service. The local connection options allow us to specify which service (Redis master group name) the connection makes requests for. In particular, we set the service name of the 'feed' connection to 'feed-service'.

For more information about Sentinel service configuration, see the Redis Sentinel Documentation.