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Connect via localhost

Connect to a localhost database/ API

With your on-premises Appsmith instance running on the same system, you may use host.docker.internal or ngrok to connect to databases, APIs, and services that are running on localhost or as other docker containers.

Using host.docker.internal

You can use host.docker.internal to connect with the databases/APIs/other docker containers running on localhost. The video below shows how to set things up.


You can also visit docker docs to read the use cases and workarounds for the host.docker.internal usage.

Connect to databases/APIs running on localhost
For Linux systems, you would need to provide a run flag `add-host`.

Only more recent versions of Docker support host-gateway, which is transformed to the Docker default bridge network IP (or virtual IP of the host).

Run the below command to test and ensure the IP address from the hosts’ file is displayed.

 run —-rm -—add-host=host.docker.internal:host-gateway

For Docker compose on Linux, you need to manually add it to the docker-compose.yaml file. Use extra hosts to add the entry as shown below:

- "host.docker.internal:host-gateway"

Using ngrok

Appsmith allows you to work with APIs and databases running on localhost using the help of ngrok. You'll have to set up ngrok for the same.

Setting ngrok

To set up 'ngrok’- you would have to signup at ngrok (it’s free!). Follow the instructions to connect your account.

Connect via ngrok

With 'ngrok,’ you would be able to connect to the databases and APIs running on your localhost.

Connect to localhost using ngrok

Connecting to a localhost database

You've a MongoDB instance running on your localhost. You wish to connect the app you are building on Appsmith Cloud to MongoDB.

Follow the below steps to connect to the MongoDB instance:

  • Expose your local MongoDB instance using ngrok command

MongoDB uses a tcp protocol for creating connections, and 27017 is the default port. If you are not using a default port, provide it in place of 27017.

ngrok tcp 27017

connect using ngrok MongoDB running on localhost

Use the host address and the port number 17392 to add a MongoDB datasource to your app.

create a MongoDB datasource using ngrok by connecting to local MongoDB

Create query

You can create queries to the newly added localhost instance of MongoDB LocalMongoDBUsingNgrok datasource.

Building a simple local API

To host an API locally, you could use a Python FastAPI server. You could install it using pip.

$ python3 -m pip install fastapi uvicorn

You could serve the API request by using the code snippet:

from fastapi import FastAPI

app = FastAPI()

items = [{
"name": "Counter-Strike",
"appid": 10,
"average_playtime": 17612,
"genres": "Action",
"price": 7.2
"name": "Team Fortress Classic",
"appid": 20,
"average_playtime": 277,
"genres": "Action",
"price": 3.99

async def root():
return items

In the code snippet - you have:

  • Imported a FastAPI library and initiated an app using the FastAPI class
  • Defined a collection of steam game objects
  • Declared a route “/” at which the items (game objects) could be accessed

You could run the server with the following command:

$ uvicorn main:app --reload

The command uvicorn main:app refers to:

  • main: the file (the Python "module").
  • app: the object created inside with the line app = FastAPI().
  • --reload: to restart the server after code changes. Only used for a development environment.

You would see a screen below when the app is up and API is ready to use.

Run the localhost API using FastAPI

Awesome, you could see your API in action.

Fire up ngrok and expose the local port[8000] to access the local API in your app available on Appsmith Cloud.


To access the API, you would have to use the HTTP protocol and port 8000.

ngrok http 8000

ngrok creates an HTTP tunnel, forwards the externally accessible address to the local address, and enables access to the local API over the internet.

connect local api using ngrok

Connect to local API

You can create an API and add the localhost API with the address

connect to an API hosted on localhost using ngrok

Next Steps

You could read the API/ query response and display the data by binding it with different widgets available on Appsmith.