Before connecting your app to the Cloud Functions emulator, make sure that
you
understand the overall Firebase Local Emulator Suite workflow
,
and that you
install and configure
the Local Emulator Suite and review its
CLI commands
.
Choose a Firebase project
The Firebase Local Emulator Suite emulates products for a single Firebase project.
To select the project to use, before you start the emulators, in the CLI run
firebase use
in your working directory. Or, you can pass
the
--project
flag to each emulator
command.
Local Emulator Suite supports emulation of
real
Firebase projects and
demo
projects.
Project type
|
Features
|
Use with emulators
|
Real
|
A real Firebase project is one you created and configured (most likely
via the Firebase console).
Real projects have live resources, like database instances, storage
buckets, functions, or any other resource you set up for that Firebase
project.
|
When working with real Firebase projects, you can run emulators for any
or all of the supported products.
For any products you are not emulating, your apps and code will
interact with the
live
resource (database instance, storage
bucket, function, etc.).
|
Demo
|
A demo Firebase project has no
real
Firebase configuration and
no live resources. These projects are usually accessed via codelabs or
other tutorials.
Project IDs for demo projects have the
demo-
prefix.
|
When working with demo Firebase projects, your apps and code interact with
emulators
only
. If your app attempts to interact with a resource
for which an emulator isn't running, that code will fail.
|
We recommend you use demo projects wherever possible. Benefits include:
- Easier setup, since you can run the emulators without ever creating a
Firebase project
- Stronger safety, since if your code accidentally invokes non-emulated
(production) resources, there is no chance of data change, usage and billing
- Better offline support, since there is no need to access the internet to
download your SDK configuration.
Instrument your app to talk to the emulators
Instrument your app for callable functions
If your prototype and test activities involve
callable backend functions
, configure interaction with the Cloud Functions for Firebase emulator like this:
Kotlin+KTX
// 10.0.2.2 is the special IP address to connect to the 'localhost' of
// the host computer from an Android emulator.
val functions = Firebase.functions
functions.useEmulator("10.0.2.2", 5001)
Java
// 10.0.2.2 is the special IP address to connect to the 'localhost' of
// the host computer from an Android emulator.
FirebaseFunctions functions = FirebaseFunctions.getInstance();
functions.useEmulator("10.0.2.2", 5001);
Swift
Functions.functions().useFunctionsEmulator(origin: "http://127.0.0.1:5001")
Web modular API
import { getApp } from "firebase/app";
import { getFunctions, connectFunctionsEmulator } from "firebase/functions";
const functions = getFunctions(getApp());
connectFunctionsEmulator(functions, "127.0.0.1", 5001);
Web namespaced API
firebase.functions().useEmulator("127.0.0.1", 5001);
Instrument your app for HTTPS functions emulation
Each HTTPS function in your code will be served from the local emulator using the following URL format:
http://
$HOST
:
$PORT
/
$PROJECT
/
$REGION
/
$NAME
For example a simple
helloWorld
function with the default host port and region would be served at:
https://localhost:5001/
$PROJECT
/us-central1/helloWorld
Instrument your app for background-triggered functions emulation
The Cloud Functions emulator supports background-triggered functions from the following sources:
- Realtime Database emulator
- Cloud Firestore emulator
- Authentication emulator
- Pub/Sub emulator
To trigger background events, modify back-end resources using the
Emulator Suite UI, or by connecting your app or test code to the emulators
using the SDK for your platform.
Test handlers for custom events emitted by Extensions
For functions you implement to handle Firebase Extensions custom events
with Cloud Functions v2, the Cloud Functions emulator pairs with the
Eventarc emulator to support
Eventarc triggers
.
To test custom event handlers for extensions that emit events, you must install
the Cloud Functions and Eventarc emulators.
The Cloud Functions runtime sets the
EVENTARC_EMULATOR
environment
variable to
localhost:9299
in the current process if the Eventarc emulator
is running. The Firebase Admin SDKs automatically connect to the Eventarc
emulator when the
EVENTARC_EMULATOR
environment variable is set. You can
modify the default port as discussed under
Configure Local Emulator Suite
.
When environment variables are properly configured, the Firebase Admin SDK
automatically sends events to the Eventarc emulator. In turn, the Eventarc
emulator makes a call back to the Cloud Functions emulator to trigger any
registered handlers.
You can check Functions logs in the Emulator Suite UI for details on
handler execution.
If your functions rely on dotenv-based
environment configuration
,
you can emulate that behavior in your local testing environment.
When using a local Cloud Functions emulator, you can override environment
variables for your project by setting up a
.env.local
file. Contents of
.env.local
take precedence over
.env
and the project-specific
.env
file.
For example, a project could include these three files containing slightly
different values for development and local testing:
.env
|
.env.dev
|
.env.local
|
PLANET=Earth
AUDIENCE=Humans
|
AUDIENCE=Dev Humans
|
AUDIENCE=Local Humans
|
When started in the local context, the emulator loads the environment
variables as shown:
$ firebase emulators:start
i emulators: Starting emulators: functions
# Starts emulator with following environment variables:
# PLANET=Earth
# AUDIENCE=Local Humans
Secrets and credentials in the Cloud Functions emulator
The Cloud Functions emulator supports the use of secrets to
store and access sensitive configuration information
.
By default, the emulator will try to access your production secrets using
application default credentials
.
In certain situations like CI environments, the emulator may fail to access
secret values due to permission restrictions.
Similar to Cloud Functions emulator support for environment variables, you can
override secrets values by setting up a
.secret.local
file. This makes it
easy for you to test your functions locally, especially if you don't have access
to the secret value.
The Cloud Functions emulator is supplemented by other prototype and test
tools:
- The Cloud Functions shell, which allows for interactive, iterative functions
prototyping and development. The shell employs the Cloud Functions emulator with
a REPL-style interface for development. No integration with the
Cloud Firestore or Realtime Database emulators is provided. Using the shell, you
mock data and perform function calls to simulate interaction with products that
the Local Emulator Suite does not currently support: Analytics,
Remote Config, and Crashlytics.
- The Firebase Test SDK for Cloud Functions, a Node.js with mocha framework
for functions development. In effect, the Cloud Functions Test SDK provides
automation atop the Cloud Functions shell.
You can find more about the Cloud Functions shell and Cloud Functions Test SDK
at
Test functions interactively
and
Unit testing of Cloud Functions
.
How the Cloud Functions emulator differs from production
The Cloud Functions emulator is fairly close to the production environment
for the majority of use cases. We've put extensive work into ensuring everything
within the Node runtime is as close to production as possible. However, the
emulator does not mimic the full containerized production environment,
so while your function code will execute realistically, other aspects of your
environment (i.e. local files, behavior after functions crashes, etc.) will
differ.
Cloud IAM
The Firebase Emulator Suite does not attempt to replicate or respect any
IAM-related behavior for running. Emulators adhere to the Firebase Security
Rules provided, but in situations where IAM would normally be used, for example
to set Cloud Functions invoking service account and thus permissions, the
emulator is not configurable and will use the globally-available account on
your developer machine, similar to running a local script directly.
Memory and processor restrictions
The emulator does not enforce memory or processor restrictions for your
functions. However, the emulator does support timing out functions via the
timeoutSeconds
runtime argument.
Note that function execution time may differ from production when functions are
run in the emulator. We recommend that after you've designed and tested
functions with the emulator, you run limited tests in production to confirm
execution times.
Planning for differences in local and production environments
Since the emulator runs on your local machine, it depends on your local
environment for applications and built-in programs and utilities.
Be aware that your local environment for Cloud Functions development may
differ from the Google production environment:
Applications you install locally to simulate the production environment (e.g.
ImageMagick from
this tutorial
)
may differ in behavior from production, especially if you require a different
versions or develop in a non-Linux environment. Consider deploying your own
binary copy of the missing program alongside your function deployment.
Similarly, built-in utilities (e.g., shell commands like
ls
,
mkdir
) may
differ from versions available in production, especially if you're developing in
a non-Linux environment (e.g., macOS). You can handle this issue by using
Node-only alternatives to native commands, or by building Linux binaries to
bundle with your deployment.
Retrying
The Cloud Functions emulator does not support retrying functions on failure.
What next?