How to Design a Configuration Cache That Handles Updates and Errors Gracefully?

Load Configuration From Files and Refresh with New Updates

Problem Statement:

A code design involves loading a configuration from files at startup and periodically refreshing it with newer versions. The aim is to have a mechanism that handles the following requirements:

• Concurrent access to the configuration
• Reloading of detected configuration changes
• Accessibility to the most recent configuration
• Immediate accessibility to the most recent configuration during updates
• Preservation of the previous configuration if an update fails

The initial design utilizes a concurrent map to store the configuration, but faces an issue where errors during updating can lead to an empty map.

Solution:

A simplified design is proposed that addresses all the requirements:

CustomerConfig Structure:

Defines the configuration to be cached:

type CustomerConfig struct {
    Data map[string]bool
    LoadedAt time.Time
}

loadConfig Function:

Loads the configuration from files:

func loadConfig() (*CustomerConfig, error) {
    cfg := &CustomerConfig{
        Data:     map[string]bool{},
        LoadedAt: time.Now(),
    }

    // Logic to load files and populate cfg.Data
    // If an error occurs, return it

    // If loading succeeds, return the config
    return cfg, nil
}

ConfigCache Structure:

Manages the configuration caching:

type ConfigCache struct {
    configMu sync.RWMutex
    config   *CustomerConfig
    closeCh  chan struct{}
}

NewConfigCache Function:

Creates a new configuration cache:

func NewConfigCache() (*ConfigCache, error) {
    cfg, err := loadConfig()
    if err != nil {
        return nil, fmt.Errorf("loading initial config failed: %w", err)
    }

    cc := &ConfigCache{
        config:  cfg,
        closeCh: make(chan struct{}),
    }

    // Launch a goroutine to periodically check for changes and load new configs
    go cc.refresher()

    return cc, nil
}

refresher Function:

Periodically checks for configuration changes and updates the cache:

func (cc *ConfigCache) refresher() {
    ticker := time.NewTicker(1 * time.Minute) // Every minute
    defer ticker.Stop()

    for {
        select {
        case <p><strong>Stop Function:</strong></p><p>Stops the refresher goroutine:</p><pre class="brush:php;toolbar:false">func (cc *ConfigCache) Stop() {
    close(cc.closeCh)
}

GetConfig Function:

Accesses the current configuration:

func (cc *ConfigCache) GetConfig() *CustomerConfig {
    cc.configMu.RLock()
    defer cc.configMu.RUnlock()
    return cc.config
}

Usage:

cc, err := NewConfigCache()
if err != nil {
    // Handle the error appropriately
}

// Access the configuration whenever needed:
cfg := cc.GetConfig()
// Use the configuration here

// Stop the cache refreshing when necessary:
cc.Stop()

This solution ensures:

• Concurrent access to the configuration
• Reload on detected changes
• Accessibility to the most recent configuration
• Immediate accessibility during updates
• Preservation of the previous configuration on update failures

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