Docker - Data and Volumes

Docker - Data and Volumes

---

Types of data

---

Container and Image Data

---

Container Data

Data can be stored inside containers as files, just as you would normally do on your local development machine.

However, once a container is removed, the data will be lost.

Note

Stopping and restarting a container will not delete your data within that container.

---

Volumes

• Volumes are folders on your host machine hard drive which are mounted (“made available”, mapped) into containers.

• Volumes persist if a container shuts down. If a container (re-)starts and mounts a volume, any data inside of that volume is available in the container.
• A container can write data into a volume and read data from it.

---

Defining Volumes

FROM node:14

WORKDIR /app

COPY package.json .

RUN npm install

COPY . .

EXPOSE 80

VOLUME [ "/app/feedback" ]

CMD ["node", "server.js"]

The VOLUME command specifies a path inside the container that will be treated as a volume. The mapping to the host’s file system is defined by the run command when starting a container.

---

Volumes & Bind Mounts

# Anonymous Volume
docker run -v /app/data ...

# Named Volume
docker run -v data:/app/data ...

# Bind Mount
docker run -v /path/to/code:/app/code

---

Volumes vs. Bind Mounts

---

Container / Volume Interaction

---

Summary

• Containers can read + write data. Volumes can help with data storage, Bind Mounts can help with direct container interaction.
• Containers can read + write data, but written data is lost if the container is removed.
• Volumes are folders on the host machine, managed by Docker, which are mounted into the container.
• Named Volumes survive container removal and can therefore be used to store persistent data.
• Anonymous Volumes are attached to a container - they can be used to save (temporary) data inside the container.
• Bind Mounts are folders on the host machine which are specified by the user and mounted into containers - like Named Volumes.