Use docker info to get arch

lib/kamal/configuration/builder.rb

@@ -29,9 +29,7 @@ class Kamal::Configuration::Builder
 
   def local_arches
     @local_arches ||= if remote
-      uname_m = `uname -m`.strip
+      arches & [ Kamal::Utils.docker_arch ]
-      local_arch = uname_m == "x86_64" ? "amd64" : uname_m
-      arches & [ local_arch ]
     else
       arches
     end

lib/kamal/utils.rb

@@ -81,4 +81,16 @@ module Kamal::Utils
   def join_commands(commands)
     commands.map(&:strip).join(" ")
   end
+
+  def docker_arch
+    arch = `docker info --format '{{.Architecture}}'`.strip
+    case arch
+    when /aarch64/
+      "arm64"
+    when /x86_64/
+      "amd64"
+    else
+      arch
+    end
+  end
 end

test/commands/builder_test.rb

@@ -145,10 +145,10 @@ class CommandsBuilderTest < ActiveSupport::TestCase
     end
 
     def local_arch
-      `uname -m`.strip == "x86_64" ? "amd64" : "arm64"
+      Kamal::Utils.docker_arch
     end
 
     def remote_arch
-      `uname -m`.strip == "x86_64" ? "arm64" : "amd64"
+      Kamal::Utils.docker_arch == "arm64" ? "amd64" : "arm64"
     end
 end

test/fixtures/deploy_with_remote_builder.yml

@@ -38,5 +38,5 @@ builder:
 readiness_delay: 0
 
 builder:
-  arch: <%= `uname -m`.strip == "x86_64" ? "arm64" : "amd64" %>
+  arch: <%= Kamal::Utils.docker_arch == "arm64" ? "amd64" : "arm64" %>
   remote: ssh://app@1.1.1.5

test/fixtures/deploy_with_remote_builder_and_custom_ports.yml

@@ -42,5 +42,5 @@ ssh:
   port: 22
 
 builder:
-  arch: <%= `uname -m`.strip == "x86_64" ? "arm64" : "amd64" %>
+  arch: <%= Kamal::Utils.docker_arch == "arm64" ? "amd64" : "arm64" %>
   remote: ssh://app@1.1.1.5:2122

test/integration/docker/deployer/app/config/deploy.yml

@@ -24,7 +24,7 @@ registry:
   password: root
 builder:
   driver: docker
-  arch: <%= uname_m = `uname -m`; uname_m == "x86_64" ? "amd64" : uname_m %>
+  arch: <%= Kamal::Utils.docker_arch %>
   args:
     COMMIT_SHA: <%= `git rev-parse HEAD` %>
 healthcheck:

test/integration/docker/deployer/app_with_roles/config/deploy.yml

@@ -18,7 +18,7 @@ registry:
   password: root
 builder:
   driver: docker
-  arch: <%= uname_m = `uname -m`; uname_m == "x86_64" ? "amd64" : uname_m %>
+  arch: <%= Kamal::Utils.docker_arch %>
   args:
     COMMIT_SHA: <%= `git rev-parse HEAD` %>
 healthcheck: