code: public void deployAll() throws MojoExecutionException {
      stager.stage();
      ImmutableList.Builder<Path> computedDeployables = ImmutableList.builder();
  
      // Look for app.yaml
      Path appYaml = deployMojo.getStagingDirectory().resolve("app.yaml");
      if (!Files.exists(appYaml)) {
        throw new MojoExecutionException("Failed to deploy all: could not find app.yaml.");
      }
      deployMojo.getLog().info("deployAll: Preparing to deploy app.yaml");
      computedDeployables.add(appYaml);
  
      // Look for config yamls
      String[] configYamls = {"cron.yaml", "dispatch.yaml", "dos.yaml", "index.yaml", "queue.yaml"};
      for (String yamlName : configYamls) {
        Path yaml = appengineDirectory.resolve(yamlName);
        if (Files.exists(yaml)) {
          deployMojo.getLog().info("deployAll: Preparing to deploy " + yamlName);
          computedDeployables.add(yaml);
        }
      }
  
      DeployConfiguration config =
          configBuilder.buildDeployConfiguration(computedDeployables.build());
  
      try {
        deployMojo.getAppEngineFactory().deployment().deploy(config);
      } catch (AppEngineException ex) {
        throw new MojoExecutionException("Failed to deploy", ex);
      }
    }
docs: Deploy a single application and any found yaml configuration files.