Customer.io SDK Patterns

Output

• A reusable SDK integration pattern with scoped configuration, schema validation, idempotency, observability, and error classification.
• A test-backed client boundary that keeps credentials and recipient data out of logs and source control.

Examples

Instantiate the client from an environment-specific secret reference, validate a synthetic event against the contract, attach a stable idempotency key, and assert the SDK call in a mocked unit test. For a development integration test, use a synthetic profile and record only result status/correlation ID; never log the client token or full event payload.

Overview

Production-ready patterns for customerio-node: type-safe wrappers with enum-constrained events, retry with exponential backoff, event batching for high-volume scenarios, and singleton lifecycle management.

Prerequisites

• customerio-node installed
• TypeScript project (recommended for type-safe patterns)
• Understanding of your event taxonomy

Instructions

Pattern 1: Type-Safe Client Wrapper

// lib/customerio-typed.ts
import { TrackClient, RegionUS, RegionEU } from "customerio-node";

// Define your event taxonomy as a union type
type CioEvent =
  | { name: "signed_up"; data: { method: string; source?: string } }
  | { name: "plan_changed"; data: { from: string; to: string; mrr: number } }
  | { name: "feature_used"; data: { feature: string; duration_ms?: number } }
  | { name: "checkout_completed"; data: { order_id: string; total: number; items: number } }
  | { name: "subscription_cancelled"; data: { reason: string; feedback?: string } };

// Define user attributes with strict types
interface CioUserAttributes {
  email: string;
  first_name?: string;
  last_name?: string;
  plan?: "free" | "starter" | "pro" | "enterprise";
  company?: string;
  created_at?: number;       // Unix seconds
  last_seen_at?: number;     // Unix seconds
  [key: string]: unknown;    // Allow additional attributes
}

export class TypedCioClient {
  private client: TrackClient;

  constructor(siteId: string, apiKey: string, region: "us" | "eu" = "us") {
    this.client = new TrackClient(siteId, apiKey, {
      region: region === "eu" ? RegionEU : RegionUS,
    });
  }

  async identify(userId: string, attributes: CioUserAttributes): Promise<void> {
    await this.client.identify(userId, {
      ...attributes,
      last_seen_at: Math.floor(Date.now() / 1000),
    });
  }

  async track(userId: string, event: CioEvent): Promise<void> {
    await this.client.track(userId, {
      name: event.name,
      data: { ...event.data, tracked_at: Math.floor(Date.now() / 1000) },
    });
  }

  async suppress(userId: string): Promise<void> {
    await this.client.suppress(userId);
  }

  async destroy(userId: string): Promise<void> {
    await this.client.destroy(userId);
  }
}

Pattern 2: Retry with Exponential Backoff

// lib/customerio-retry.ts
interface RetryOptions {
  maxRetries: number;
  baseDelayMs: number;
  maxDelayMs: number;
  jitterFactor: number;  // 0 to 1
}

const DEFAULT_RETRY: RetryOptions = {
  maxRetries: 3,
  baseDelayMs: 1000,
  maxDelayMs: 30000,
  jitterFactor: 0.3,
};

async function withRetry<T>(
  fn: () => Promise<T>,
  opts: RetryOptions = DEFAULT_RETRY
): Promise<T> {
  let lastError: Error | undefined;

  for (let attempt = 0; attempt <= opts.maxRetries; attempt++) {
    try {
      return await fn();
    } catch (err: any) {
      lastError = err;
      const statusCode = err.statusCode ?? err.status;

      // Don't retry client errors (except 429 rate limit)
      if (statusCode >= 400 && statusCode < 500 && statusCode !== 429) {
        throw err;
      }

      if (attempt === opts.maxRetries) break;

      // Exponential backoff with jitter
      const delay = Math.min(
        opts.baseDelayMs * Math.pow(2, attempt),
        opts.maxDelayMs
      );
      const jitter = delay * opts.jitterFactor * Math.random();
      await new Promise((r) => setTimeout(r, delay + jitter));
    }
  }
  throw lastError;
}

// Usage with Customer.io client
import { TrackClient, RegionUS } from "customerio-node";

const cio = new TrackClient(
  process.env.CUSTOMERIO_SITE_ID!,
  process.env.CUSTOMERIO_TRACK_API_KEY!,
  { region: RegionUS }
);

// Wrap any operation with retry
await withRetry(() =>
  cio.identify("user-123", { email: "user@example.com" })
);

await withRetry(() =>
  cio.track("user-123", { name: "page_viewed", data: { url: "/pricing" } })
);

Pattern 3: Event Queue with Batching

// lib/customerio-batch.ts
import { TrackClient, RegionUS } from "customerio-node";

interface QueuedEvent {
  userId: string;
  name: string;
  data?: Record<string, any>;
}

export class CioBatchTracker {
  private queue: QueuedEvent[] = [];
  private timer: NodeJS.Timeout | null = null;
  private client: TrackClient;

  constructor(
    private readonly batchSize: number = 50,
    private readonly flushIntervalMs: number = 5000
  ) {
    this.client = new TrackClient(
      process.env.CUSTOMERIO_SITE_ID!,
      process.env.CUSTOMERIO_TRACK_API_KEY!,
      { region: RegionUS }
    );
    this.startTimer();
  }

  enqueue(userId: string, name: string, data?: Record<string, any>): void {
    this.queue.push({ userId, name, data });
    if (this.queue.length >= this.batchSize) {
      this.flush();
    }
  }

  async flush(): Promise<void> {
    if (this.queue.length === 0) return;
    const batch = this.queue.splice(0, this.batchSize);
    const concurrency = 10;

    for (let i = 0; i < batch.length; i += concurrency) {
      const chunk = batch.slice(i, i + concurrency);
      await Promise.allSettled(
        chunk.map((event) =>
          this.client.track(event.userId, {
            name: event.name,
            data: event.data,
          })
        )
      );
    }
  }

  private startTimer(): void {
    this.timer = setInterval(() => this.flush(), this.flushIntervalMs);
  }

  async shutdown(): Promise<void> {
    if (this.timer) clearInterval(this.timer);
    await this.flush();
  }
}

// Usage
const tracker = new CioBatchTracker(50, 5000);

// Non-blocking — events are queued and flushed automatically
tracker.enqueue("user-1", "page_viewed", { url: "/home" });
tracker.enqueue("user-2", "button_clicked", { button: "cta" });

// On process exit
process.on("SIGTERM", async () => {
  await tracker.shutdown();
  process.exit(0);
});

Pattern 4: Singleton with Validation

// lib/customerio-singleton.ts
import { TrackClient, APIClient, RegionUS, RegionEU } from "customerio-node";

class CioClientFactory {
  private static trackInstance: TrackClient | null = null;
  private static appInstance: APIClient | null = null;

  static getTrackClient(): TrackClient {
    if (!this.trackInstance) {
      const siteId = process.env.CUSTOMERIO_SITE_ID;
      const apiKey = process.env.CUSTOMERIO_TRACK_API_KEY;
      if (!siteId || !apiKey) {
        throw new Error(
          "Missing CUSTOMERIO_SITE_ID or CUSTOMERIO_TRACK_API_KEY. " +
          "Set these in your environment or .env file."
        );
      }
      const region = process.env.CUSTOMERIO_REGION === "eu" ? RegionEU : RegionUS;
      this.trackInstance = new TrackClient(siteId, apiKey, { region });
    }
    return this.trackInstance;
  }

  static getAppClient(): APIClient {
    if (!this.appInstance) {
      const appKey = process.env.CUSTOMERIO_APP_API_KEY;
      if (!appKey) {
        throw new Error(
          "Missing CUSTOMERIO_APP_API_KEY. " +
          "Set this in your environment or .env file."
        );
      }
      const region = process.env.CUSTOMERIO_REGION === "eu" ? RegionEU : RegionUS;
      this.appInstance = new APIClient(appKey, { region });
    }
    return this.appInstance;
  }

  /** Reset for testing */
  static reset(): void {
    this.trackInstance = null;
    this.appInstance = null;
  }
}

// Usage — same instance everywhere
const cio = CioClientFactory.getTrackClient();
const api = CioClientFactory.getAppClient();

Pattern Summary

Pattern	When to Use	Key Benefit
Typed Client	Always	Compile-time safety on events + attributes
Retry + Backoff	Production API calls	Handles transient 5xx and 429 errors
Batch Queue	High-volume tracking (>100 events/sec)	Reduces connection overhead, respects rate limits
Singleton Factory	Multi-module apps	Prevents connection leaks, validates config once

Error Handling

Error	Cause	Solution
Type mismatch	Wrong event data shape	Use TypeScript union types for events
Queue memory growth	Events produced faster than flushed	Lower batchSize, increase flush frequency
Retry exhausted (3x)	Persistent API failure	Check credentials, Customer.io status page
Singleton null credentials	Env vars not loaded	Ensure dotenv loads before client creation

Resources

• customerio-node SDK
• Track API Rate Limits
• About Customer.io APIs

Next Steps

After implementing patterns, proceed to customerio-primary-workflow for messaging workflows.