How to debug with `docker exec`?

To debug a running Docker container using docker exec, you can follow these steps:

Identify the Running Container: First, list the running containers to find the one you want to debug.
```
docker ps
```
Access the Container's Shell: Use docker exec to start an interactive shell session inside the container. This allows you to run commands directly within the container's environment.
```
docker exec -it <container_name_or_id> /bin/bash
```
or, if the container uses a different shell:
```
docker exec -it <container_name_or_id> /bin/sh
```
Inspect the Environment: Once inside the container, you can check the environment, installed packages, and configuration files. For example:
```
# Check the current working directory
pwd

# List files in the directory
ls -la

# Check installed packages (for Debian/Ubuntu)
dpkg -l
```
Run Diagnostic Commands: You can run commands to diagnose issues, such as checking logs, testing network connectivity, or inspecting running processes:
```
# Check application logs
cat /var/log/app.log

# Test network connectivity to another container
curl http://other-container:port
```
Modify Configuration: If necessary, you can modify configuration files or environment variables directly within the container to troubleshoot issues.
Exit the Container: Once you have finished debugging, you can exit the shell session by typing:
```
exit
```

Using docker exec in this way allows you to interactively debug issues within a running container, making it easier to identify and resolve problems.