Docker Codeigniter3 cannot connect with SQL server database - sql-server

Question

I am new to docker and I am trying to deploy docker container on my local machine. However, Codeigniter3 cannot connect with the SQL server database.
Dockerfile:
FROM php:7.4.23-apache
WORKDIR /var/www/html
COPY src/ .
USER root
RUN chmod 777 ./system
RUN chown -R www-data:www-data /var/www/html
RUN a2enmod rewrite
ENV ACCEPT_EULA=Y
RUN apt-get update && apt-get install -y nano wget curl gnupg2
RUN curl https://packages.microsoft.com/keys/microsoft.asc | apt-key add -
RUN curl https://packages.microsoft.com/config/ubuntu/20.04/prod.list >
/etc/apt/sources.list.d/mssql-release.list
RUN apt-get update
RUN apt-get -y --no-install-recommends install msodbcsql17 unixodbc-dev
RUN pecl install sqlsrv
RUN pecl install pdo_sqlsrv
RUN docker-php-ext-enable sqlsrv pdo_sqlsrv
RUN echo "extension=pdo_sqlsrv.so" >> `php --ini | grep "Scan for additional .ini files" | sed -e "s|.*:\s*||"`/30-pdo_sqlsrv.ini
RUN echo "extension=sqlsrv.so" >> `php --ini | grep "Scan for additional .ini files" |
sed -e "s|.*:\s*||"`/30-sqlsrv.ini
RUN service apache2 restart
docker-compose.yaml
version: '3.9'
services:
app:
build: .
container_name: ci-mssql-db-app
image: ci-mssql-db-app:1.0.0
ports:
- 80:80
depends_on:
- db
links:
- db
db:
container_name: mssql
image: mcr.microsoft.com/mssql/server:2019-CU12-ubuntu-20.04
restart: always
environment:
ACCEPT_EULA: "Y"
SA_PASSWORD: "Testing123"
MSSQL_PID: "Developer"
Codeigniter3 database.php file configuration:
$db['default'] = array(
'dsn' => '',
'hostname' => 'db:1433',
'username' => 'admin',
'password' => 'admin',
'database' => 'ciapp',
'dbdriver' => 'sqlsrv',
'dbprefix' => '',
'pconnect' => FALSE,
'db_debug' => (ENVIRONMENT !== 'production'),
'cache_on' => FALSE,
'cachedir' => '',
'char_set' => 'utf8',
'dbcollat' => 'utf8_general_ci',
'swap_pre' => '',
'encrypt' => FALSE,
'compress' => FALSE,
'stricton' => FALSE,
'failover' => array(),
'save_queries' => TRUE
);
Here, I have set hostname = 'db:1433' as it points to the service name so that it will get the ip address of db service automatically. And, SQL server runs on 1433 port by default.
After running the docker command
docker-compose up --build
I am getting this error,
Unable to connect to your database server using the provided settings.
Error Image Link
I am struggling to solve it for almost two weeks. Please help me in this regard.