java.net.UnknownHostException: host.docker.internal: Name or service not known on AWS EC2 - spring-boot

Question

I ran into this "java.net.UnknownHostException: host.docker.internal: Name or service not known" problem when deploying a dockerized spring boot application on an AWS EC2 T2.micro instance. The spring boot application failed to start because of this error.
But the weird part is, I did not use the variable "host.docker.internal" anywhere in my application: not in the code, not in the yaml file, not in the .env file:
$ sudo grep -Rl "host.docker.internal" ~
/home/ec2-user/.bash_history
And when I run the following command it shows nothing but previous command to search for it:
$ cat /home/ec2-user/.bash_history | grep "host.docker.internal"
Locally I am using Windows 10 for development, and I can successfully bring up the stack with docker-compose.
Here is the EC2 instance OS version info:
$ cat /etc/*release
NAME="Amazon Linux"
VERSION="2"
ID="amzn"
ID_LIKE="centos rhel fedora"
VERSION_ID="2"
PRETTY_NAME="Amazon Linux 2"
ANSI_COLOR="0;33"
CPE_NAME="cpe:2.3:o:amazon:amazon_linux:2"
HOME_URL="https://amazonlinux.com/"
Amazon Linux release 2 (Karoo)
And here is the docker-compose file that I used on the EC2 instance:
version: '2'
services:
backend:
container_name: backend
image: 'dockerhubuser/backend:0.0.4'
ports:
- '8080:8080'
volumes:
- /var/log/backend/logs:/var/log/backend/logs
- ./backend-ssl:/etc/ssh/backend
env_file:
- .env
depends_on:
- mysql
- redis
redis:
container_name: redis
image: 'redis:alpine'
ports:
- '6379:6379'
volumes:
- $PWD/redis/redis-data:/var/lib/redis
- $PWD/redis/redis.conf:/usr/local/etc/redis/redis.conf
mysql:
container_name: mysql
image: 'mysql:8.0.21'
ports:
- '3306:3306'
environment:
MYSQL_DATABASE: dbname
MYSQL_USER: dbuser
MYSQL_PASSWORD: dbpass
MYSQL_ROOT_PASSWORD: dbrootpass
volumes:
- ./my_volume/mysql:/var/lib/mysql
volumes:
my_volume:
And here is my .env file on the EC2 instance:
SERVER_PORT=8080
KEY_STORE=/etc/ssh/backend/keystore.p12
KEY_STORE_PASSWORD=keystorepass
REDIS_HOST=redis
REDIS_PORT=6379
DB_HOST=mysql
DB_PORT=3306
DB_USERNAME=dbuser
DB_PASSWORD=dbpass
I am pretty sure that this .env file is being used when bringing up the stack with "docker-compose up" because I can see the SERVER_PORT in the log matches this file when I change it.
2021-01-02 20:55:44.870 [main] INFO o.s.b.w.e.tomcat.TomcatWebServer - Tomcat initialized with port(s): 8080 (https)
But I keep getting the error complaining about "host.docker.internal".
Here are things that I have tried but not working:
Hard-code the db host in property spring.datasource.url in application.yml
Add the following entry to /etc/hosts file (see https://stackoverflow.com/a/48547074/1852496)
172.17.0.1 host.docker.internal
Add the following entry to /etc/hosts file, where "ip-172-31-33-56.us-east-2.compute.internal" is what I got when running command "echo $HOSTNAME"
ip-172-31-33-56.us-east-2.compute.internal host.docker.internal
Terminate the instance and created another T2.micro instance, but got same result.
Edit inbound rules to allow TCP:3306 from anywhere.
Can someone take a look? Any help appreciated.

Answer 1

It works on Ubuntu 20.04 after adding "172.17.0.1 host.docker.internal" to /etc/hosts file.
Make sure the docker engine version is 20.10-beta1 or newer.