ExposeInvalidFormat

Table of contents

Output

EXPOSE instruction should not define an IP address or host-port mapping, found '127.0.0.1:80:80'

Description

The EXPOSE instruction in a Dockerfile is used to indicate which ports the container listens on at runtime. It should not include an IP address or host-port mapping, as this is not the intended use of the EXPOSE instruction. Instead, it should only specify the port number and optionally the protocol (TCP or UDP).

Important

This will become an error in a future release.

Examples

❌ Bad: IP address and host-port mapping used.

FROM alpine
EXPOSE 127.0.0.1:80:80

✅ Good: only the port number is specified.

FROM alpine
EXPOSE 80

❌ Bad: Host-port mapping used.

FROM alpine
EXPOSE 80:80

✅ Good: only the port number is specified.

FROM alpine
EXPOSE 80