From 74e0614b5c5fa877944cb3c6d213a6fd3a910186 Mon Sep 17 00:00:00 2001
From: Tom Wilkie <tom.wilkie@gmail.com>
Date: Tue, 9 Feb 2021 14:50:36 +0000
Subject: [PATCH] Add instructions for building docker image locally to
 README.md

Fixes #8442

Signed-off-by: Tom Wilkie <tom.wilkie@gmail.com>
---
 .gitignore |  1 +
 README.md  | 12 +++++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index 617a2e5dd..c31d513e2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,3 +23,4 @@ npm_licenses.tar.bz2
 /web/ui/assets_vfsdata.go
 
 /vendor
+/.build
diff --git a/README.md b/README.md
index 23e26051b..c84dffb7b 100644
--- a/README.md
+++ b/README.md
@@ -91,9 +91,19 @@ The Makefile provides several targets:
   * *test-short*: run the short tests
   * *format*: format the source code
   * *vet*: check the source code for common errors
-  * *docker*: build a docker container for the current `HEAD`
   * *assets*: build the new experimental React UI
 
+### Building the Docker image
+
+The `make docker` target is designed for use in our CI system.
+You can build a docker image locally with the following commands:
+
+    $ make promu
+    $ promu crossbuild -p linux/amd64
+    $ make common-docker-amd64
+
+*NB* if you are on a Mac, you will need [gnu-tar](https://formulae.brew.sh/formula/gnu-tar).
+
 ## React UI Development
 
 For more information on building, running, and developing on the new React-based UI, see the React app's [README.md](https://github.com/prometheus/prometheus/blob/master/web/ui/react-app/README.md).