---
title: Use containers for R development
linkTitle: Develop your app
weight: 20
keywords: R, local, development
description: Learn how to develop your R application locally.
aliases:
  - /language/r/develop/
  - /guides/language/r/develop/
---

## Prerequisites

Complete [Containerize a R application](containerize.md).

## Overview

In this section, you'll learn how to set up a development environment for your containerized application. This includes:

- Adding a local database and persisting data
- Configuring Compose to automatically update your running Compose services as you edit and save your code

## Get the sample application

You'll need to clone a new repository to get a sample application that includes logic to connect to the database.

Change to a directory where you want to clone the repository and run the following command.

```console
$ git clone https://github.com/mfranzon/r-docker-dev.git
```

## Configure the application to use the database

To try the connection between the Shiny application and the local database you have to modify the `Dockerfile` changing the `COPY` instruction:

```diff
-COPY src/ .
+COPY src_db/ .
```

## Add a local database and persist data

You can use containers to set up local services, like a database. In this section, you'll update the `compose.yaml` file to define a database service and a volume to persist data.

In the cloned repository's directory, open the `compose.yaml` file in an IDE or text editor.

In the `compose.yaml` file, you need to un-comment the properties for configuring the database. You must also mount the database password file and set an environment variable on the `shiny-app` service pointing to the location of the file in the container.

The following is the updated `compose.yaml` file.

```yaml
services:
  shiny-app:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - 3838:3838
    environment:
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    depends_on:
      db:
        condition: service_healthy
    secrets:
      - db-password
  db:
    image: postgres
    restart: always
    user: postgres
    secrets:
      - db-password
    volumes:
      - db-data:/var/lib/postgresql/data
    environment:
      - POSTGRES_DB=example
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    expose:
      - 5432
    healthcheck:
      test: ["CMD", "pg_isready"]
      interval: 10s
      timeout: 5s
      retries: 5
volumes:
  db-data:
secrets:
  db-password:
    file: db/password.txt
```

> [!NOTE]
>
> To learn more about the instructions in the Compose file, see [Compose file
> reference](/reference/compose-file/).

Before you run the application using Compose, notice that this Compose file specifies a `password.txt` file to hold the database's password. You must create this file as it's not included in the source repository.

In the cloned repository's directory, create a new directory named `db` and inside that directory create a file named `password.txt` that contains the password for the database. Using your favorite IDE or text editor, add the following contents to the `password.txt` file.