Running the Datastore Emulator

The Datastore emulator provides local emulation of the production Datastore environment. You can use the emulator to develop and test your application locally. In addition, the emulator can help you generate indexes for your production Firestore in Datastore mode instance and delete unneeded indexes. This page guides you through installing the emulator, starting the emulator, and setting environment variables to connect your application to the emulator.

Before you begin

To use the Datastore emulator you need:

A Java JRE (version 8 or greater)
The Google Cloud SDK
An application built using the Google Cloud Client Libraries

Installing the emulator

The Datastore emulator is a component of the Google Cloud SDK's gcloud tool. Use the gcloud components install command to install the Datastore emulator:

gcloud components install cloud-datastore-emulator

Emulator data directories

The emulator simulates Datastore by creating /WEB-INF/appengine-generated/local_db.bin in a specified data directory and storing data in local_db.bin. By default, the emulator uses the data directory ~/.config/gcloud/emulators/datastore/. The local_db.bin file persists between sessions of the emulator. You can set up multiple data directories and think of each as a separate, local Datastore mode instance. To clear the contents of a local_db.bin file, stop the emulator and manually delete the file.

Starting the emulator

Start the emulator by executing datastore start from a command prompt:

gcloud beta emulators datastore start [flags]

where [flags] are optional command-line arguments supplied to the gcloud tool. For example:

--data-dir=[DATA_DIR] changes the emulator's data directory. The emulator creates the /WEB-INF/appengine-generated/local_db.bin file inside [DATA_DIR] or, if available, uses an existing file.
--no-store-on-disk configures the emulator not to persist any data to disk for the emulator session.

See the gcloud beta emulators datastore start reference for the full list of optional flags.

After you start the emulator, you should see a message similar to the following:

...
[datastore] Dev App Server is now running.

To stop the emulator, type Control-C at the command prompt.

Setting environment variables

After you start the emulator, you need to set environment variables so that your application connects to the emulator instead of your production Datastore mode database. Set these environment variables on the same machine that you use to run your application.

You need to set the environment variables each time you start the emulator. The environment variables depend on dynamically assigned port numbers that could change when you restart the emulator.

Automatically setting the variables

If your application and the emulator run on the same machine, you can set the environment variables automatically:

Linux / macOS

Run env-init using command substitution:

$(gcloud beta emulators datastore env-init)

Windows

Create and run a batch file using output from env-init:

gcloud beta emulators datastore env-init > set_vars.cmd && set_vars.cmd

Your application will now connect to the Datastore emulator.

Manually setting the variables

If your application and the emulator run on different machines, set the environment variables manually:

Run the env-init command:

gcloud beta emulators datastore env-init

On the machine that runs your application, set the environment variables and values as directed by the output of the env-init command. For example:
Linux / macOS
```
export DATASTORE_EMULATOR_HOST=localhost:8432
export DATASTORE_PROJECT_ID=my-project-id
```
Windows
```
set DATASTORE_EMULATOR_HOST=localhost:8432
set DATASTORE_PROJECT_ID=my-project-id
```

Your application will now connect to the Datastore emulator.

Updating and deleting indexes

By running your application using the emulator, you can generate indexes for your production Datastore mode database, as well as delete unneeded indexes. Learn more at Using the gcloud tool.

Removing environment variables

After you finish using the emulator, stop the emulator (Control-C) and remove the environment variables so your application will connect to your production Datastore mode database.

Automatically removing the variables

If your application and the emulator run on the same machine, you can remove the environment variables automatically:

Linux / macOS

Run env-unset using command substitution:

$(gcloud beta emulators datastore env-unset)

Windows

Create and run a batch file using output from env-unset:

gcloud beta emulators datastore env-unset > remove_vars.cmd && remove_vars.cmd

Your application will now connect to your production Datastore mode database.

Manually removing the variables

If your application and the emulator run on different machines, remove the environment variables manually:

Run the env-unset command:

gcloud beta emulators datastore env-unset

On the machine that runs your application, remove the environment variables as directed by the output of the env-unset command. For example:
Linux / macOS
```
unset DATASTORE_EMULATOR_HOST
unset DATASTORE_PROJECT_ID
```
Windows
```
set DATASTORE_EMULATOR_HOST=
set DATASTORE_PROJECT_ID=
```

Your application will now connect to your production Datastore mode database.