Error parsing reference: "ubuntu:18.04 as base" is not a valid repository/tag

I had a dockerfile in a repository for a while now and I built it several times in the past week.

It has this line at the top of the file:

FROM ubuntu:18.04 AS builder

Today I started getting this error:

Step 1/1 : FROM ubuntu:18.04 AS builder
Error parsing reference: "ubuntu:18.04 AS builder" is not a valid repository/tag: invalid reference format

I haven’t touched the Dockerfile in that repo in a while. Nobody has touched that file in 5 months.

I ran this command to build it:

docker build .

Docker version:

bash-3.2$ docker --version
Docker version 17.03.1-ce-rc1, build 3476dbf

What am I doing wrong here.

>Solution :

Docker multi stage builds (keyword AS) were introduced in 17.06. You are using 17.03, so you need to switch to the newer docker version.