My frontend can connect to my backend inside the container in EC2, but not when testing via the IP address

Question

Good morning,

I am trying to upload my local website into EC2 using docker containers. I am building two images (1 for front-end and 1 for back-end) in docker and then pull these images in EC2.
I have also created a database in RDS.
I have configured everything:
* The backend connection to the database
* The connection frontend and backend
* The domain name linked to the IP address of my EC2 instance

When going to the IP address of my website, I can see my frontend. I have a login tab. And when I try to login I have a :
`Failed to load resource: net::ERR_NAME_NOT_RESOLVED : backend:8080/api/auth/signin:1 `

To resolve this issue, I have tried several times to :
* Build the images
* Inspect the frontend environment variables
* To verify the network configuration: my containers are attached to the same network
* Verify Environment Variable in Container: so going into my frontend container and checking. Everything is normal.

And I also tested the connectivity to the backend when I am inside my frontend container using the following commands:

```
docker exec -it frontend curl -X POST http://backend:8080/api/auth/signin -H "Content-Type: application/json" -d '{"username": "...", "password": "..."}'
```
And this querry worked perfectly.
So my frontend can communicate with my backend and database using command lines in the terminal.

But when I use the login page, I can't connect.

I have tried to solve this issue for 1 week now, but I am out of options.

It would be nice to have some help or some clues to be able to login into my website.

Thank you in advance,
Alexia

NARRAVULA MUNISAI TEJA · Answer

Hello,

Your frontend can't find the backend by name. Try these steps:

* Replace "backend" in login URL with the actual IP address of your backend container (if it works with IP, it's a DNS issue).

* Ensure your containers share a network where "backend" resolves to the correct IP.

* Check if your frontend code expects an IP or hostname, and update the login request accordingly.

**Update Security Group:** Ensure the security group associated with your EC2 instance allows inbound traffic on the port your backend uses (e.g., port 80 for HTTP or port 443 for HTTPS).

```
# Allow HTTP traffic
Type:   HTTP
Port:   80
Source: 0.0.0.0/0

# Allow HTTPS traffic
Type:   HTTPS
Port:   443
Source: 0.0.0.0/0
```

Riku_Kobayashi · Answer

Hello.

The front end code itself runs on the browser, so I think you will get an error even if you access it using the Docker container name.  
In other words, if you change the part specifying “backend:8080” in the front end to something such as an EC2 Public IP address, you should be able to access the site.  
https://stackoverflow.com/questions/77635244/failed-to-load-resource-neterr-name-not-resolved-error

victor · Answer

Have u solved the problem? I'm having the same issue.

My frontend can connect to my backend inside the container in EC2, but not when testing via the IP address

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