Question 1

What is the difference between a Docker volume and a bind mount?

Accepted Answer

Both make data survive a container being removed, and they differ in who manages the storage.

A bind mount maps a specific path on the host into the container. You control exactly where the data lives, and you can read and edit it with ordinary tools. This makes it ideal for development, where mounting your source directory means edits appear inside the container immediately without rebuilding.

A volume is managed by Docker in an area it controls. You refer to it by name rather than by path. Because Docker owns it, it works identically across operating systems, can be backed up and moved with Docker commands, and can use storage drivers for network or cloud storage.

The practical differences that matter:

- Portability. A bind mount hardcodes a host path, so a compose file using one may not work on a colleague machine or on a server. A named volume works anywhere.
- Permissions. Bind mounts carry host ownership into the container, which frequently causes permission errors when the container user differs from your host user. Volumes are initialised with the image directory ownership, which usually just works.
- Performance. On Linux both are essentially native. On macOS and Windows, where containers run in a virtual machine, bind mounts cross a filesystem boundary and can be dramatically slower for workloads with many small file operations, such as installing dependencies. This surprises people moving between platforms.
- Initial contents. A new volume mounted over a non-empty image directory is populated from that directory. A bind mount hides whatever was there.

The common convention is bind mounts for source code in development, and named volumes for databases and anything the application writes.

Question 2

What is the difference between a Docker image and a container?

Accepted Answer

An image is a static, read-only template. A container is a running, or stopped, instance created from one. The relationship is close to that between a program on disk and a process running it: one

Question 3

Why can my Docker container not connect to a service on localhost?

Accepted Answer

Inside a container, localhost means the container itself, not the machine running it. Each container has its own network namespace and its own loopback interface, so a connection to localhost from

Question 4

What is the difference between COPY and ADD in a Dockerfile?

Accepted Answer

Both instructions move files from the build context into the image, and for ordinary files they behave identically. The difference is that ADD has two extra behaviours that trigger automatically, and

Question 5

Why is my Docker image so large and how do I shrink it?

Accepted Answer

Image size is the sum of every layer, and layers are immutable. That second point catches people out: deleting a file in a later instruction does not reclaim the space, because the earlier layer

Question 6

What is the difference between a process and a thread?

Accepted Answer

A process is an independent running program with its own memory space. A thread is a unit of execution inside a process, sharing that process's memory with its sibling threads. What a process owns:

Question 7

How to set up a Docker container for a Node.js app?

Accepted Answer

Setting up a Docker container for a Node.js app involves creating a Dockerfile, building the image, and running the container. This ensures a consistent environment for your application.

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