> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Demo Docker Container Operations Continued
> This lesson covers advanced Docker flags and best practices for managing containers effectively.
In this lesson, we’ll explore advanced Docker flags and best practices for managing containers. You’ll learn how to:
* Automatically clean up ephemeral containers
* Customize container hostnames
* Control container restarts with various policies
* Inspect Docker events for troubleshooting
* Copy files between host and containers
* Expose ports using random and static mappings
***
## Automatically Remove Ephemeral Containers with `--rm`
When running short-lived or CI/CD containers, you can use `--rm` to automatically delete them upon exit. This helps keep your environment clean and free of stale containers.
```bash theme={null}
docker container run -itd --name=kodekloud --rm ubuntu
docker container ls -l # Lists only the most recent container
```
Stop and watch it disappear:
```bash theme={null}
docker container stop kodekloud
```
Using `--rm` is ideal for one-off or CI tasks. Remember that you won’t be able to inspect logs or the filesystem after the container exits.
***
## Setting Container Name vs. Hostname
Docker allows you to assign both a unique container name and an internal hostname:
```bash theme={null}
docker container run -itd \
--name=yogesh \
--hostname=kodekloud \
--rm ubuntu
docker container ls -l
docker exec -it yogesh hostname
```
> Container names must be unique per host, but you can reuse the same internal hostname across multiple containers.
***
## Restart Policies
Docker’s `--restart` flag offers fine-grained control over container uptime. Below is a summary of each policy:
| Policy | Description |
| ---------------- | ------------------------------------------------------------------------------- |
| `no` | (default) Container will **not** restart after exit. |
| `on-failure[:N]` | Restart only on non-zero exit status. Optionally limit retries to `N`. |
| `always` | Always restart the container regardless of exit code or Docker daemon restarts. |
| `unless-stopped` | Like `always`, but the container won’t restart if you manually stopped it. |
### 1. `--restart=no` (Default)
```bash theme={null}
docker container run -itd --name=caseone --restart=no ubuntu
docker container stop caseone
docker container ls -l
```
The container will remain stopped until you manually start it again.
### 2. `--restart=on-failure`
```bash theme={null}
docker container run -itd --name=casetwo --restart=on-failure ubuntu
docker container kill casetwo # Simulate a failure
sleep 2
docker container ls -l
```
The container automatically restarts if it exits with a non-zero status.
### 3. `--restart=always`
```bash theme={null}
docker container run -itd --name=casethree --restart=always ubuntu
docker container stop casethree
docker container ls -l
```
Regardless of exit reason or daemon restart, the container will be restarted.
### 4. `--restart=unless-stopped`
```bash theme={null}
docker container run -itd --name=casefour --restart=unless-stopped ubuntu
docker container stop casefour
docker container ls -l
```
Even if Docker restarts, `casefour` stays down after a manual stop.
Use `always` or `unless-stopped` for critical services. Excessive restart loops on failure can degrade performance—consider `on-failure` with a retry limit.
***
## Inspecting Docker Events
To diagnose restart loops or networking events, view real-time Docker system events:
```bash theme={null}
docker system events --since 60m
```
Sample output:
2020-05-04T08:38:43.747Z network connect cf10… (container=2daf…, name=bridge)
2020-05-04T08:38:43.976Z container start … (image=ubuntu, name=casethree)
2020-05-04T08:39:43.633Z network connect cf10… (container=74b0…, name=bridge)
2020-05-04T08:39:43.890Z container start … (image=ubuntu, name=casefour)
***
## Copying Files Between Host and Container (`docker cp`)
You don’t need an interactive shell to move files; `docker cp` handles it directly.
### Host → Container
```bash theme={null}
mkdir -p /var/temp
echo "hello for KodeKloud" > /var/temp/yogishtest
docker container run -itd --name=copytest --rm ubuntu
docker container exec copytest mkdir -p /root
docker container cp /var/temp/yogishtest copytest:/root/
docker container exec -it copytest cat /root/yogishtest
```
### Container → Host
```bash theme={null}
docker container exec copytest bash -c "mkdir -p /var/temp && echo 'container to host' > /var/temp/docker-host"
docker container cp copytest:/var/temp/docker-host /var/temp/
ls -l /var/temp/docker-host
cat /var/temp/docker-host
```
***
## Publishing Ports
By default, containers don’t expose ports to the host. You can use random or static port mappings:
| Option | Description | Access URL |
| ------ | --------------------------------------------------- | --------------------------- |
| none | No mapping; container ports are isolated | Unreachable from host |
| `-P` | Random high host port mapped to container’s port | `http://:` |
| `-p` | Static host-to-container port mapping (e.g., 82:80) | `http://:82` |
### No Port Mapping
```bash theme={null}
docker container run -itd --name=case1 httpd
docker container ls -l
```
Accessing via host IP will fail.
### Random Port Mapping (`-P`)
```bash theme={null}
docker container run -itd -P --name=case2 httpd
docker container ls -l
```
Docker picks a random port (e.g., 32768) for container port 80.
### Static Port Mapping (`-p`)
```bash theme={null}
docker container run -itd --name=case3 -p 82:80 httpd
docker container ls -l
```
Now host port 82 forwards to container port 80.
### Port Mapping on Restart
```bash theme={null}
docker container restart case2
docker container restart case3
docker container ls -l
```
* With `-P`, Docker may assign a different random port after restart.
* With `-p`, the mapping remains consistent.
For production services, always use `-p` for predictable port assignments and easier firewall configuration.
***
## References
* [Docker Run Reference](https://docs.docker.com/engine/reference/commandline/run/)
* [Docker Container CP](https://docs.docker.com/engine/reference/commandline/cp/)
* [Docker Restart Policies](https://docs.docker.com/config/containers/start-containers-automatically/)
We hope this lesson helps you master advanced Docker container operations!