feat(orchestrator): automatic provider fallback with runner availability check

Adds built-in load balancing: check GitHub runner availability before
builds start, auto-route to a fallback provider when runners are busy
or offline. Eliminates the need for a separate check-runner job.

New inputs: fallbackProviderStrategy, runnerCheckEnabled,
runnerCheckLabels, runnerCheckMinAvailable.

Outputs providerFallbackUsed and providerFallbackReason for workflow
visibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/model/build-parameters.ts

@@ -54,6 +54,10 @@ class BuildParameters {
   public sshAgent!: string;
   public sshPublicKeysDirectoryPath!: string;
   public providerStrategy!: string;
+  public fallbackProviderStrategy!: string;
+  public runnerCheckEnabled!: boolean;
+  public runnerCheckLabels!: string[];
+  public runnerCheckMinAvailable!: number;
   public gitPrivateToken!: string;
   public awsStackName!: string;
   public awsEndpoint?: string;
@@ -194,6 +198,10 @@ class BuildParameters {
       containerRegistryRepository: Input.containerRegistryRepository,
       containerRegistryImageVersion: Input.containerRegistryImageVersion,
       providerStrategy: OrchestratorOptions.providerStrategy,
+      fallbackProviderStrategy: OrchestratorOptions.fallbackProviderStrategy,
+      runnerCheckEnabled: OrchestratorOptions.runnerCheckEnabled,
+      runnerCheckLabels: OrchestratorOptions.runnerCheckLabels,
+      runnerCheckMinAvailable: OrchestratorOptions.runnerCheckMinAvailable,
       buildPlatform: OrchestratorOptions.buildPlatform,
       kubeConfig: OrchestratorOptions.kubeConfig,
       containerMemory: OrchestratorOptions.containerMemory,

src/model/orchestrator/options/orchestrator-options.ts

@@ -138,6 +138,24 @@ class OrchestratorOptions {
     return provider || 'local';
   }
 
+  static get fallbackProviderStrategy(): string {
+    return OrchestratorOptions.getInput('fallbackProviderStrategy') || '';
+  }
+
+  static get runnerCheckEnabled(): boolean {
+    return OrchestratorOptions.getInput('runnerCheckEnabled') === 'true';
+  }
+
+  static get runnerCheckLabels(): string[] {
+    const labels = OrchestratorOptions.getInput('runnerCheckLabels');
+
+    return labels ? labels.split(',').map((l) => l.trim()) : [];
+  }
+
+  static get runnerCheckMinAvailable(): number {
+    return Number(OrchestratorOptions.getInput('runnerCheckMinAvailable')) || 1;
+  }
+
   static get containerCpu(): string {
     return OrchestratorOptions.getInput('containerCpu') || `1024`;
   }

src/model/orchestrator/orchestrator.ts

@@ -20,6 +20,7 @@ import { FollowLogStreamService } from './services/core/follow-log-stream-servic
 import OrchestratorResult from './services/core/orchestrator-result';
 import OrchestratorOptions from './options/orchestrator-options';
 import ResourceTracking from './services/core/resource-tracking';
+import { RunnerAvailabilityService } from './services/core/runner-availability-service';
 
 class Orchestrator {
   public static Provider: ProviderInterface;
@@ -76,6 +77,40 @@ class Orchestrator {
   private static async setupSelectedBuildPlatform() {
     OrchestratorLogger.log(`Orchestrator platform selected ${Orchestrator.buildParameters.providerStrategy}`);
 
+    // Check runner availability and apply fallback if needed
+    if (Orchestrator.buildParameters.runnerCheckEnabled && Orchestrator.buildParameters.fallbackProviderStrategy) {
+      const owner = OrchestratorOptions.githubOwner;
+      const repo = OrchestratorOptions.githubRepoName;
+      const token = Orchestrator.buildParameters.gitPrivateToken || process.env.GITHUB_TOKEN || '';
+
+      OrchestratorLogger.log(
+        `Checking runner availability (labels: [${Orchestrator.buildParameters.runnerCheckLabels.join(', ')}], min: ${Orchestrator.buildParameters.runnerCheckMinAvailable})`,
+      );
+
+      const result = await RunnerAvailabilityService.checkAvailability(
+        owner,
+        repo,
+        token,
+        Orchestrator.buildParameters.runnerCheckLabels,
+        Orchestrator.buildParameters.runnerCheckMinAvailable,
+      );
+
+      OrchestratorLogger.log(
+        `Runner check: ${result.totalRunners} total, ${result.matchingRunners} matching, ${result.idleRunners} idle — ${result.reason}`,
+      );
+
+      if (result.shouldFallback) {
+        const original = Orchestrator.buildParameters.providerStrategy;
+        const fallback = Orchestrator.buildParameters.fallbackProviderStrategy;
+        OrchestratorLogger.log(`Falling back from '${original}' to '${fallback}' — ${result.reason}`);
+        Orchestrator.buildParameters.providerStrategy = fallback;
+        core.setOutput('providerFallbackUsed', 'true');
+        core.setOutput('providerFallbackReason', result.reason);
+      } else {
+        core.setOutput('providerFallbackUsed', 'false');
+      }
+    }
+
     // Detect LocalStack endpoints and handle AWS provider appropriately
     // AWS_FORCE_PROVIDER options:
     //   - 'aws': Force AWS provider (requires LocalStack Pro with ECS support)

src/model/orchestrator/services/core/runner-availability-service.ts

@@ -0,0 +1,142 @@
+import { Octokit } from '@octokit/core';
+import OrchestratorLogger from './orchestrator-logger';
+
+interface GitHubRunner {
+  id: number;
+  name: string;
+  status: 'online' | 'offline';
+  busy: boolean;
+  labels: Array<{ name: string }>;
+}
+
+interface RunnerCheckResult {
+  shouldFallback: boolean;
+  reason: string;
+  totalRunners: number;
+  matchingRunners: number;
+  idleRunners: number;
+}
+
+/**
+ * Checks GitHub Actions runner availability to support automatic provider fallback.
+ *
+ * When a user configures `runnerCheckEnabled: true` with a `fallbackProviderStrategy`,
+ * this service queries the GitHub API for runner status before the build starts.
+ * If insufficient runners are available, the orchestrator routes to the fallback provider.
+ */
+export class RunnerAvailabilityService {
+  /**
+   * Check if enough runners are available to handle the build.
+   *
+   * @param owner - GitHub repository owner
+   * @param repo - GitHub repository name
+   * @param token - GitHub token with repo/actions scope
+   * @param requiredLabels - Labels runners must have (empty = any runner)
+   * @param minAvailable - Minimum idle runners required
+   * @returns RunnerCheckResult with decision and diagnostics
+   */
+  static async checkAvailability(
+    owner: string,
+    repo: string,
+    token: string,
+    requiredLabels: string[],
+    minAvailable: number,
+  ): Promise<RunnerCheckResult> {
+    if (!token) {
+      return {
+        shouldFallback: false,
+        reason: 'No GitHub token available — skipping runner check',
+        totalRunners: 0,
+        matchingRunners: 0,
+        idleRunners: 0,
+      };
+    }
+
+    try {
+      const octokit = new Octokit({ auth: token });
+
+      // Fetch all runners for the repository
+      const runners = await RunnerAvailabilityService.fetchRunners(octokit, owner, repo);
+
+      if (runners.length === 0) {
+        return {
+          shouldFallback: true,
+          reason: 'No runners registered for this repository',
+          totalRunners: 0,
+          matchingRunners: 0,
+          idleRunners: 0,
+        };
+      }
+
+      // Filter by required labels
+      const matching = RunnerAvailabilityService.filterByLabels(runners, requiredLabels);
+
+      // Count idle (online + not busy)
+      const idle = matching.filter((r) => r.status === 'online' && !r.busy);
+
+      const result: RunnerCheckResult = {
+        shouldFallback: idle.length < minAvailable,
+        reason:
+          idle.length >= minAvailable
+            ? `${idle.length} idle runner(s) available (need ${minAvailable})`
+            : `Only ${idle.length} idle runner(s) available, need ${minAvailable}`,
+        totalRunners: runners.length,
+        matchingRunners: matching.length,
+        idleRunners: idle.length,
+      };
+
+      return result;
+    } catch (error: any) {
+      // If the API call fails (permissions, rate limit, etc.), don't block the build
+      OrchestratorLogger.log(`Runner availability check failed: ${error.message}`);
+
+      return {
+        shouldFallback: false,
+        reason: `Runner check failed (${error.message}) — proceeding with primary provider`,
+        totalRunners: 0,
+        matchingRunners: 0,
+        idleRunners: 0,
+      };
+    }
+  }
+
+  /**
+   * Fetch all runners for a repository, handling pagination.
+   */
+  private static async fetchRunners(octokit: Octokit, owner: string, repo: string): Promise<GitHubRunner[]> {
+    const allRunners: GitHubRunner[] = [];
+    let page = 1;
+    const perPage = 100;
+
+    while (true) {
+      const response = await octokit.request('GET /repos/{owner}/{repo}/actions/runners', {
+        owner,
+        repo,
+        per_page: perPage,
+        page,
+      });
+
+      const runners = (response.data.runners || []) as GitHubRunner[];
+      allRunners.push(...runners);
+
+      if (runners.length < perPage) break;
+      page++;
+    }
+
+    return allRunners;
+  }
+
+  /**
+   * Filter runners by required labels. A runner matches if it has ALL required labels.
+   * If requiredLabels is empty, all runners match.
+   */
+  private static filterByLabels(runners: GitHubRunner[], requiredLabels: string[]): GitHubRunner[] {
+    if (requiredLabels.length === 0) return runners;
+
+    return runners.filter((runner) => {
+      const runnerLabelNames = runner.labels.map((l) => l.name.toLowerCase());
+
+      return requiredLabels.every((required) => runnerLabelNames.includes(required.toLowerCase()));
+    });
+  }
+}