ERROR 2002 (HY000): Can't connect to MySQL server on 'db' (115) - mysql

Question

I am trying to move existing project to Docker. I followed this tutorial at M.Academy and followed the setup instructions from Docker on Existing Project
While executing trying to connect with MySQL I am getting this error ERROR 2002 (HY000): Can't connect to MySQL server on 'db' (115)
I also tried to execute: telnet db 3306
Response:
Trying 172.17.0.1...
telnet: Unable to connect to remote host: Connection timed out
I tried everything but couldn't figure out the problem. I am new to Docker. I am using Ubuntu 18.04 LTE. Haven't changed db.env and got no error on any other step before importing the database.
I further checked and found out that the container is not able to establish connection with MySQL.
P.S. I am successfully able to connect with same MySQL service outside Docker container by using (external MySQL port) mysql -h 127.0.01 -u root -p -P 3306
Steps To Reproduce
Install Docker & Docker Compose on Ubuntu 18.04
Download the Docker Compose template: curl -s https://raw.githubusercontent.com/markshust/docker-magento/master/lib/template | bash
Replace with existing source code of your existing Magento instance: cp -R ~/Sites/existing src
Execute: docker-compose -f docker-compose.yml up -d
Copy files to container: bin/copytocontainer --all
Import existing database: bin/mysql < /var/www/magento243.sql
Expected Result
Database should have been successfully imported
Actual Result
ERROR 2002 (HY000): Can't connect to MySQL server on 'db' (115)
P.S. Issue has already been raised here: https://github.com/markshust/docker-magento/issues/589
docker-compose.yml
version: "3"
services:
app:
image: markoshust/magento-nginx:1.18-5
ports:
- "80:8000"
- "443:8443"
depends_on:
- "db"
volumes: &appvolumes
- ~/.composer:/var/www/.composer:cached
- ~/.ssh/id_rsa:/var/www/.ssh/id_rsa:cached
- ~/.ssh/known_hosts:/var/www/.ssh/known_hosts:cached
- appdata:/var/www/html
- sockdata:/sock
- ssldata:/etc/nginx/certs
extra_hosts: &appextrahosts
## M1 Mac support to fix Docker delay, see #566
- "app:172.17.0.1"
- "phpfpm:172.17.0.1"
- "db:172.17.0.1"
- "redis:172.17.0.1"
- "elasticsearch:172.17.0.1"
- "rabbitmq:172.17.0.1"
## Selenium support, replace "magento.test" with URL of your site
- "magento.test:172.17.0.1"
phpfpm:
image: markoshust/magento-php:7.4-fpm-11
volumes: *appvolumes
extra_hosts: *appextrahosts
env_file: env/phpfpm.env
db:
image: mariadb:10.4
command: --max_allowed_packet=256M
ports:
- "3306:3306"
env_file: env/db.env
volumes:
- dbdata:/var/lib/mysql
extra_hosts: *appextrahosts
redis:
image: redis:5.0-alpine
ports:
- "6379:6379"
extra_hosts: *appextrahosts
elasticsearch:
image: markoshust/magento-elasticsearch:7.9.3-1
ports:
- "9200:9200"
- "9300:9300"
environment:
- "discovery.type=single-node"
## Set custom heap size to avoid memory errors
- "ES_JAVA_OPTS=-Xms1g -Xmx1g"
## Avoid test failures due to small disks
## More info at https://github.com/markshust/docker-magento/issues/488
- "cluster.routing.allocation.disk.threshold_enabled=false"
- "index.blocks.read_only_allow_delete"
extra_hosts: *appextrahosts
rabbitmq:
image: rabbitmq:3.8.22-management-alpine
ports:
- "15672:15672"
- "5672:5672"
volumes:
- rabbitmqdata:/var/lib/rabbitmq
environment:
- RABBITMQ_VM_MEMORY_HIGH_WATERMARK=1GB
extra_hosts: *appextrahosts
mailcatcher:
image: sj26/mailcatcher
ports:
- "1080:1080"
extra_hosts: *appextrahosts
## Selenium support, uncomment to enable
#selenium:
# image: selenium/standalone-chrome-debug:3.8.1
# ports:
# - "5900:5900"
# extra_hosts: *appextrahosts
volumes:
appdata:
dbdata:
rabbitmqdata:
sockdata:
ssldata:

Answer 1

This issue was finally resolved by
Removing extra_hosts entries from the YML file
Adding networks in YML
Final docker-compose.yml
version: "3"
services:
app:
image: markoshust/magento-nginx:1.18-5
ports:
- "81:8000"
- "444:8443"
depends_on:
- "db"
volumes: &appvolumes
- ~/.composer:/var/www/.composer:cached
- ~/.ssh/id_rsa:/var/www/.ssh/id_rsa:cached
- ~/.ssh/known_hosts:/var/www/.ssh/known_hosts:cached
- appdata:/var/www/html
- sockdata:/sock
- ssldata:/etc/nginx/certs
networks:
- customNetwork
phpfpm:
image: markoshust/magento-php:7.4-fpm-11
volumes: *appvolumes
env_file: env/phpfpm.env
networks:
- customNetwork
db:
image: mariadb:10.4
command: --max_allowed_packet=256M
ports:
- "3307:3306"
env_file: env/db.env
volumes:
- dbdata:/var/lib/mysql
networks:
- customNetwork
redis:
image: redis:5.0-alpine
ports:
- "6379:6379"
networks:
- customNetwork
elasticsearch:
image: markoshust/magento-elasticsearch:7.9.3-1
ports:
- "9201:9200"
- "9301:9300"
environment:
- "discovery.type=single-node"
## Set custom heap size to avoid memory errors
- "ES_JAVA_OPTS=-Xms1g -Xmx1g"
## Avoid test failures due to small disks
## More info at https://github.com/markshust/docker-magento/issues/488
- "cluster.routing.allocation.disk.threshold_enabled=false"
- "index.blocks.read_only_allow_delete"
networks:
- customNetwork
rabbitmq:
image: rabbitmq:3.8.22-management-alpine
ports:
- "15672:15672"
- "5672:5672"
volumes:
- rabbitmqdata:/var/lib/rabbitmq
environment:
- RABBITMQ_VM_MEMORY_HIGH_WATERMARK=1GB
networks:
- customNetwork
mailcatcher:
image: sj26/mailcatcher
ports:
- "1080:1080"
networks:
- customNetwork
volumes:
appdata:
dbdata:
rabbitmqdata:
sockdata:
ssldata:
networks:
customNetwork: