The simplest way to use the emulated realtime database from an existing client is to set export FIREBASE_DATABASE_EMULATOR_HOST=localhost:9000. If you are passing a credential to admin.initializeApp you may also want to create a conditional to allow for it to not be passed through as it's not needed for the emulator. You still need to keep the databaseURL but it can be set to the real instance. The emulator will extract the name out of the URL and create a local emulated database.
If you have custom rules, they can be added to the rules.json.
Additional firebase services can be emulated with the same stack by simply adding them to the firebase.json, for example:
{
"database": {
"rules": "rules.json"
},
"hosting": {
"target": "staging",
"public": "dist/web-ui",
"ignore": [
"firebase.json",
"**/.*",
"**/node_modules/**"
],
"rewrites": [
{
"source": "**",
"destination": "/index.html"
}
]
},
"emulators": {
"database": {
"port": "9000",
"host": "0.0.0.0"
},
"ui": {
"port": "4000",
"host": "0.0.0.0"
},
"firestore": {
"port": "8080",
"host": "0.0.0.0"
},
"auth": {
"port": "9099",
"host": "0.0.0.0"
},
"hosting": {
"port": "50033",
"host": "0.0.0.0"
},
"storage": {
"port": "9199",
"host": "0.0.0.0"
}
}
}