The WORKDIR instruction

Learn to set the container working directory with WORKDIR.

The WORKDIR instruction

WORKDIR sets the directory where the following RUN, CMD, ENTRYPOINT, COPY and ADD instructions run. If the directory doesn't exist it is created. RUN cd /app doesn't work, because each RUN runs in a new shell:

# wrong: cd doesn't carry over to the next line
RUN cd /app
RUN npm install       # runs in /

# right
WORKDIR /app
RUN npm install

Relative WORKDIR

WORKDIR can be used several times; relative paths are appended to the previous one. Using absolute paths improves readability:

WORKDIR /app
WORKDIR src        # now /app/src
RUN pwd            # /app/src

WORKDIR becomes the starting directory when you enter the container with docker exec.

Exercise Installing in the right directory

Write a Dockerfile based on node:20-alpine: WORKDIR /app; copy the package*.json files to ./; run npm ci --omit=dev; copy the whole project; CMD is node server.js in exec form.

Show example solution

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --omit=dev
COPY . .
CMD ["node", "server.js"]

Test yourself

Which directory do RUN cd /app followed by RUN ls list?
- The previous WORKDIR (/ by default)
- /app
- It errors
- Empty output
Show answer

The previous WORKDIR (/ by default) — Each RUN instruction is a separate shell process.
Set the directory for the following instructions.
```
____ /app
```
Show answer
```
WORKDIR /app
```
Match.

WORKDIR /app

Sets and creates the directory
RUN cd /app

Only for that RUN
WORKDIR src

Relative: appended to the previous
docker exec

Starts in WORKDIR

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