CAST AI SDK Patterns

Overview

CAST AI uses a REST API with X-API-Key header authentication. There is no official SDK -- build typed wrappers around fetch or requests. These patterns cover singleton clients, typed responses, retry with backoff, and multi-cluster management.

Prerequisites

• Completed castai-install-auth setup
• TypeScript 5+ or Python 3.10+
• Familiarity with async/await patterns

Instructions

Step 1: TypeScript API Client

// src/castai/client.ts
interface CastAIConfig {
  apiKey: string;
  baseUrl?: string;
  timeoutMs?: number;
}

interface CastAICluster {
  id: string;
  name: string;
  status: string;
  providerType: "eks" | "gke" | "aks";
  agentStatus: string;
  createdAt: string;
}

interface CastAISavings {
  monthlySavings: number;
  savingsPercentage: number;
  currentMonthlyCost: number;
  optimizedMonthlyCost: number;
}

interface CastAINode {
  name: string;
  instanceType: string;
  lifecycle: "on-demand" | "spot";
  allocatableCpu: string;
  allocatableMemory: string;
  zone: string;
}

class CastAIClient {
  private apiKey: string;
  private baseUrl: string;
  private timeoutMs: number;

  constructor(config: CastAIConfig) {
    this.apiKey = config.apiKey;
    this.baseUrl = config.baseUrl ?? "https://api.cast.ai";
    this.timeoutMs = config.timeoutMs ?? 30000;
  }

  private async request<T>(path: string, options?: RequestInit): Promise<T> {
    const controller = new AbortController();
    const timeout = setTimeout(() => controller.abort(), this.timeoutMs);

    try {
      const response = await fetch(`${this.baseUrl}${path}`, {
        ...options,
        headers: {
          "X-API-Key": this.apiKey,
          "Content-Type": "application/json",
          ...options?.headers,
        },
        signal: controller.signal,
      });

      if (!response.ok) {
        const body = await response.text();
        throw new CastAIError(response.status, body, path);
      }

      return response.json();
    } finally {
      clearTimeout(timeout);
    }
  }

  async listClusters(): Promise<CastAICluster[]> {
    const data = await this.request<{ items: CastAICluster[] }>(
      "/v1/kubernetes/external-clusters"
    );
    return data.items;
  }

  async getSavings(clusterId: string): Promise<CastAISavings> {
    return this.request(`/v1/kubernetes/clusters/${clusterId}/savings`);
  }

  async listNodes(clusterId: string): Promise<CastAINode[]> {
    const data = await this.request<{ items: CastAINode[] }>(
      `/v1/kubernetes/external-clusters/${clusterId}/nodes`
    );
    return data.items;
  }

  async updatePolicies(clusterId: string, policies: Record<string, unknown>): Promise<void> {
    await this.request(`/v1/kubernetes/clusters/${clusterId}/policies`, {
      method: "PUT",
      body: JSON.stringify(policies),
    });
  }
}

class CastAIError extends Error {
  constructor(
    public readonly status: number,
    public readonly body: string,
    public readonly path: string
  ) {
    super(`CAST AI ${status} on ${path}: ${body}`);
    this.name = "CastAIError";
  }

  get retryable(): boolean {
    return this.status === 429 || this.status >= 500;
  }
}

Step 2: Singleton with Retry

// src/castai/index.ts
let instance: CastAIClient | null = null;

export function getCastAIClient(): CastAIClient {
  if (!instance) {
    if (!process.env.CASTAI_API_KEY) {
      throw new Error("CASTAI_API_KEY environment variable required");
    }
    instance = new CastAIClient({ apiKey: process.env.CASTAI_API_KEY });
  }
  return instance;
}

export async function withRetry<T>(
  fn: () => Promise<T>,
  maxRetries = 3
): Promise<T> {
  for (let attempt = 0; attempt <= maxRetries; attempt++) {
    try {
      return await fn();
    } catch (err) {
      if (attempt === maxRetries) throw err;
      if (err instanceof CastAIError && !err.retryable) throw err;
      const delay = 1000 * Math.pow(2, attempt) + Math.random() * 500;
      await new Promise((r) => setTimeout(r, delay));
    }
  }
  throw new Error("Unreachable");
}

Step 3: Python Client

# castai_client.py
import os
import time
import requests
from dataclasses import dataclass
from typing import Optional

@dataclass
class CastAIConfig:
    api_key: str
    base_url: str = "https://api.cast.ai"
    timeout: int = 30

class CastAIClient:
    def __init__(self, config: Optional[CastAIConfig] = None):
        self.config = config or CastAIConfig(
            api_key=os.environ["CASTAI_API_KEY"]
        )
        self.session = requests.Session()
        self.session.headers.update({
            "X-API-Key": self.config.api_key,
            "Content-Type": "application/json",
        })

    def _get(self, path: str) -> dict:
        resp = self.session.get(
            f"{self.config.base_url}{path}",
            timeout=self.config.timeout,
        )
        resp.raise_for_status()
        return resp.json()

    def list_clusters(self) -> list[dict]:
        return self._get("/v1/kubernetes/external-clusters")["items"]

    def get_savings(self, cluster_id: str) -> dict:
        return self._get(f"/v1/kubernetes/clusters/{cluster_id}/savings")

    def list_nodes(self, cluster_id: str) -> list[dict]:
        return self._get(
            f"/v1/kubernetes/external-clusters/{cluster_id}/nodes"
        )["items"]

    def get_policies(self, cluster_id: str) -> dict:
        return self._get(f"/v1/kubernetes/clusters/{cluster_id}/policies")

Error Handling

Status	Meaning	Action
401	Invalid API key	Rotate key at console.cast.ai
403	Insufficient permissions	Use Full Access key
404	Cluster not found	Verify cluster ID
429	Rate limited	Backoff and retry
5xx	Server error	Retry with exponential backoff

Resources

• CAST AI OpenAPI Spec
• CAST AI Terraform Provider Source

Next Steps

Apply these patterns in castai-core-workflow-a to manage cluster optimization.