Firebase Cloud Functions

Expose Genkit flows as Firebase Cloud Functions using OnCallGenkit. This lets you deploy AI-powered functions that scale automatically on Google Cloud.

Installation

<dependency>
    <groupId>com.google.genkit</groupId>
    <artifactId>genkit-plugin-firebase</artifactId>
    <version>1.0.0-SNAPSHOT</version>
</dependency>

You also need the Cloud Functions Framework:

<dependency>
    <groupId>com.google.cloud.functions</groupId>
    <artifactId>functions-framework-api</artifactId>
    <version>1.1.0</version>
    <scope>provided</scope>
</dependency>

Creating a Cloud Function

import com.google.cloud.functions.HttpFunction;
import com.google.cloud.functions.HttpRequest;
import com.google.cloud.functions.HttpResponse;
import com.google.genkit.Genkit;
import com.google.genkit.ai.GenerateOptions;
import com.google.genkit.plugins.firebase.FirebasePlugin;
import com.google.genkit.plugins.firebase.functions.OnCallGenkit;
import com.google.genkit.plugins.googlegenai.GoogleGenAIPlugin;

public class GeneratePoemFunction implements HttpFunction {
    private final OnCallGenkit genkitFunction;

    public GeneratePoemFunction() {
        Genkit genkit = Genkit.builder()
            .plugin(GoogleGenAIPlugin.create(System.getenv("GEMINI_API_KEY")))
            .plugin(FirebasePlugin.builder().build())
            .build();

        genkit.defineFlow("generatePoem", String.class, String.class,
            (ctx, topic) -> genkit.generate(GenerateOptions.builder()
                .model("googleai/gemini-2.0-flash")
                .prompt("Write a poem about: " + topic)
                .build()).getText());

        this.genkitFunction = OnCallGenkit.fromFlow(genkit, "generatePoem");
    }

    @Override
    public void service(HttpRequest request, HttpResponse response)
            throws IOException {
        genkitFunction.service(request, response);
    }
}

Authentication and App Check

OnCallGenkit supports Firebase Authentication and App Check for securing your functions:

this.genkitFunction = OnCallGenkit.fromFlow(genkit, "generatePoem")
    .withAuthPolicy(authContext -> {
        if (authContext.getUid() == null) {
            throw new RuntimeException("Authentication required");
        }
    })
    .enforceAppCheck(true)
    .consumeAppCheckToken(true)
    .withCors("https://myapp.example.com");

Auth policy options

Method	Description
withAuthPolicy(policy)	Validate the Firebase Auth context before running the flow
enforceAppCheck(true)	Reject requests without a valid App Check token
consumeAppCheckToken(true)	Consume the App Check token (replay protection)
withCors(origin)	Set allowed CORS origins

Streaming responses

OnCallGenkit automatically supports streaming via Server-Sent Events (SSE). Clients that send requests with Accept: text/event-stream receive chunked responses.

Deploying

Deploy with the Google Cloud CLI:

gcloud functions deploy generatePoem \
  --runtime java21 \
  --trigger-http \
  --entry-point=com.example.GeneratePoemFunction \
  --set-env-vars GEMINI_API_KEY=your-key

Or deploy with the Firebase CLI:

firebase deploy --only functions

Requirements

• Firebase project on the Blaze (pay-as-you-go) plan
• Application Default Credentials or a service account JSON
• GCLOUD_PROJECT or GOOGLE_CLOUD_PROJECT environment variable (auto-detected)
• Java 21 runtime

Sample

See the firebase sample for a Cloud Functions deployment example.