a9s Redis SPI Configuration

This document describes a9s Redis SPI configuration.

Summary

Custom Parameter Configuration

The a9s Redis SPI handles custom parameters for all service instances. It does configuration and validation of custom parameters.

The a9s Redis SPI defines default values for certain custom parameters. Also, it defines whether a custom parameter can be set by the application developer.

The platform operator can overwrite those choices by changing the a9s Redis SPI configuration. The platform operator has to configure the property redis-spi.service_instance.custom_param_config. The property value must be a hash. Every key in that hash stands for a custom parameter and the value for every key contains the configuration for that particular parameter. The configuration for a particular param is a hash consisting of the following optional keys: default_value and modifiable. The key default_value specifies the default value for that parameter and modifiable specifies whether the application developer is allowed to set that custom parameter. For example:

redis-spi:
  service_instance:
    custom_param_config:
      maxclients:
        default_value: 6000
        modifiable: false

Default Custom Parameter Configuration

The following table contains custom parameters that are configurable by the platform operator. The meaning of those custom parameters can be read in the application developer documentation for a9s Redis.

NameDefault valueIs modifiable
lazyfree-lazy-eviction'no'true
lazyfree-lazy-expire'no'true
lua-time-limit5000true
maxclients10000true
maxmemory-policy'volatile-lru'true
maxmemory-samples5true
notify-keyspace-events''true

Example Configuration

Let's build an imaginary example.

The default value for the maxclients custom parameter should be 600. The custom parameter lua-time-limit should also have a default value of 600 and the application developer should not be allowed to change it.

Then the configuration must look the following way:

redis-spi:
  service_instance:
    custom_param_config:
      maxclients:
        default_value: 600
        modifiable: true
      lua-time-limit:
        default_value: 600
        modifiable: false

Notes

Additional custom parameters will be made available over time. We do not make all available custom parameters the SPIs know available to the platform operator from the beginning.

During the SPI startup, the configuration the platform operator made will be checked. When it's invalid, the SPI will not start up.