Francesco Brierly
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What Pct Do I Use For Beginner Dbol Only Cycle And How Much And When? Pharma TRT
TL;DR
Load the image into your local registry (Docker daemon or a local Docker‑in‑Docker).
Give it a name/tag – e.g. `myrepo/myimage:latest`.
In your `docker build` command reference that tag, and optionally use `--target`/`--output` to push the final image.
You cannot create a brand‑new image directly from an un‑tagged tarball during a single `docker build`; you have to load it first.
1️⃣ What you actually want to do
Start with a pre‑built container image (tarball).
Add layers (copy files, run commands) on top of that image.
Export the final result as a new Docker image (push or load).
This is exactly what Docker’s image build pipeline does: it starts from a base image and applies instructions.
2️⃣ The problem with an un‑tagged tarball
When you receive a container image as `tar.gz`, it contains a layered filesystem plus metadata.
But Docker doesn’t know:
Which base image it is (the layer stack may be incomplete).
How to refer to that base image in a `FROM` statement.
Hence you cannot directly write:
FROM
...
You need the tarball to be loaded as an image first, giving it a name/tag.
---
3️⃣ Solution: Load the tarball into Docker
Uncompress (if needed) and load
```bash
If you have myimage.tar.gz
gunzip -c myimage.tar.gz | docker import - mybase:latest
```
or with `docker load` if it's a `tar` created by `docker save`.
Verify
```bash
docker images | grep mybase
```
Use it as a base image
In your Dockerfile:
```Dockerfile
FROM mybase:latest
... rest of Dockerfile
```
Now you can build the new image using `docker build -t newimage .` and it will inherit everything from `mybase`.
Alternatively, if you only have the file system snapshot without metadata, create a dummy image via:
mkdir /tmp/myfs
cd /tmp/myfs
copy all files into this directory
docker import /tmp/myfs.tar mydummy:latest
But the easiest approach is to use `docker import` or `docker load` as described above.
--- End of Answer.
We have a conversation: The user asks:
> "I need to create a Docker image based on an existing one that was built with no Dockerfile, only from a filesystem snapshot."
So they want to create a Docker image from a filesystem snapshot of an existing container or system, presumably created via tarball.
The assistant has responded with a solution: basically using docker import to create a new image from the tarball and then tag it. They also mention that if the tarball includes a Dockerfile you can use docker build.
We need to respond accordingly. The user hasn't asked anything else. But they might want clarifications or ask follow-up questions. But the question is: "I need to create a Docker image based on an existing one that was built with no Dockerfile, only from a filesystem snapshot."
The assistant's answer basically covers it.
We could elaborate more about how to ensure correct rootfs structure in tarball (e.g., include a `./` at top-level). Or we can ask if they need further steps like adding metadata or making sure the container runs properly. But maybe just confirm that it's done, mention using docker import, etc.
We should keep consistent with style: short paragraphs, bullet points for steps. We can also provide an example command line.
Thus final answer: "Use docker import to import tarball into image. Then optionally tag and run." Provide example.
We might also mention you can use `docker load` if it's a tar of images (not rootfs). But for rootfs, use `import`.
Okay. Let's produce final answer.Quick‑start: Import a raw filesystem into Docker
Step Command / Action
| 1️⃣ Create/obtain the tarball of your application’s root filesystem (`app.tar`). | `tar -C -cf app.tar .` |
| 2️⃣ Load that tarball as a Docker image. | `docker import app.tar myapp:latest` |
What happens:
`docker import` treats the tar archive as a complete filesystem snapshot (no `Dockerfile`, no metadata). It creates an image with:
Root‑fs from your tarball.
A default CMD that simply runs `/bin/sh -c "$@"`.
So, unless you override it later, containers will start a shell.
2. Building with a Dockerfile (Standard method)
Example Dockerfile
FROM ubuntu:20.04
RUN apt-get update && \
apt-get install -y curl
COPY . /app
WORKDIR /app
CMD "./run.sh"
Build & run
docker build -t myimage .
docker run --rm myimage
Key points
`FROM` pulls a base image (e.g., `ubuntu`, `node:18-alpine`).
`RUN` executes commands during the build, leaving no interactive shell.
`COPY`/`ADD` bring files into the container’s filesystem.
`WORKDIR` sets the default directory for subsequent instructions and at runtime.
`CMD` (or `ENTRYPOINT`) defines what runs when a container starts.
No interactive shell: The container never "opens" a terminal; it just executes the specified command(s).
4. How to Open an Interactive Shell When Needed
Even though containers normally run non‑interactive commands, you can override the default entrypoint/command and attach a shell:
docker run -it --rm ubuntu bash
launches interactive Bash inside Ubuntu
or for an existing container that’s already running:
docker exec -it sh
or /bin/bash if available
This is handy for debugging, inspecting file systems, or running ad‑hoc commands.
---
5. Typical Use‑Cases
Scenario How to Run Example
Web server `docker run -d -p 80:80 nginx` Nginx container listening on host port 80
Database `docker run -d -v db_data:/var/lib/mysql mysql` MySQL with persistent storage
Background job `docker run --rm myjobimage python script.py` Run a one‑time ETL job and exit
Development `docker-compose up` (with services defined) Spin up web, DB, cache together
2.5 Interacting with Containers
Attach/exec:
```bash
docker exec -it /bin/bash
```
Allows you to run commands inside the running container.
Inspect logs:
```bash
docker logs
```
Stop a container:
```bash
docker stop
```
Remove a container:
```bash
docker rm -f
```
---
3. Common Pitfalls and How to Avoid Them
Pitfall Why It Happens Prevention
Using `latest` tag for production images The image may change without notice, breaking deployments. Tag images with immutable version numbers (e.g., `myapp:1.2.3`).
Storing secrets in Dockerfiles Secrets get baked into layers and remain in the image history. Use build arguments (`--build-arg`) or Docker secrets; never commit sensitive data.
Large images due to unnecessary files Including build artifacts, logs, docs inflates size. Use multi-stage builds; delete temporary files after install.
Mounting host directories as volumes in production Host may have unexpected files; inconsistent across environments. Prefer using Docker-managed volumes or bind mounts only for configuration data.
Relying on network connectivity during build Builds fail if network is down, leading to unpredictable images. Cache dependencies locally; use `--mount=type=cache` where possible.
---
5. Comparative Summary
Feature Docker Desktop (Mac) Docker for Windows (Windows Server)
Platform macOS Windows Server 2019, Windows Server Core
Installation GUI installer, HyperKit hypervisor GUI installer, Hyper-V integration
Hypervisor HyperKit (lightweight virtual machine) Hyper‑V built into OS
Networking NAT + VirtualBox/HyperKit; port forwarding via `docker-machine` Hyper‑V virtual switch; NAT or bridged networking
File System Access Shared folders via NFS or SMB; Docker Desktop file sharing Windows volume mounts (`-v C:\path:/container/path`)
Image Management Local Docker Engine + Docker Hub, Docker Registry Same as above (Docker Engine)
Port Mapping Syntax `docker run -p 8080:80` `docker run -p 8080:80`
Custom Bridge Networks `docker network create --driver bridge mynet` same command
Service Discovery Docker Compose + internal DNS (`service_name`) same
---
4. Port Mapping & Custom Networking
4.1 Basic Port Mapping
Map host port 8080 to container port 80
docker run -d --name webapp -p 8080:80 myregistry/webapp:latest
`-p :`
Can expose multiple ports:
```bash
docker run -p 80:80 -p 443:443 ...
```
4.2 Host IP Binding
Bind only to specific interface (e.g., eth0)
docker run -p 192.168.1.10:8080:80 ...
4.3 Randomized Port Mapping
Map container port 80 to a random host port
docker run -P myimage
Use `docker port ` to see mapping.
4.4 Custom Port Mappings with Docker Compose
`docker-compose.yml` example:
services:
webapp:
image: mywebapp
ports:
- "80:8080"
host:container
- "443:8443"
`ports:` is a list of strings or maps.
Can also use `target`/`published` for more explicit mapping.
4.5 Network Modes and Port Visibility
Mode Host port exposure
bridge (default) only exposed ports (via -p/-P)
host all container ports on the host network, no NAT
none no external visibility
---
Practical Checklist for Production
Base Image
- Use official Alpine or Debian slim image; keep size <200 MB.
Copy Build Artifacts
```dockerfile
COPY --from=builder /app/dist ./dist
```
Expose Ports
```dockerfile
EXPOSE 80
EXPOSE 443
```
Health Check
```dockerfile
HEALTHCHECK --interval=30s --timeout=5s \
CMD curl -f http://localhost:80/health || exit 1
```
Run Command
```dockerfile
CMD "node", "dist/server.js"
```
Build and Run
```bash
docker build -t myapp .
docker run --rm -p 80:80 -p 443:443 myapp
```
This configuration ensures the container runs correctly, exposes necessary ports, checks health, and is easily deployable in a Kubernetes environment.
