Simplify the builders configuration

1. Add driver as an option, defaulting to `docker-container`. For a
   "native" build you can set it to `docker`
2. Set arch as a array of architectures to build for, defaulting to
   `[ "amd64", "arm64" ]` unless you are using the docker driver in
   which case we default to not setting a platform
3. Remote is now just a connection string for the remote builder
4. If remote is set, we only use it for non-local arches, if we are
   only building for the local arch, we'll ignore it.

Examples:

On arm64, build for arm64 locally, amd64 remotely or
On amd64, build for amd64 locally, arm64 remotely:

```yaml
builder:
  remote: ssh://docker@docker-builder
```

On arm64, build amd64 on remote,
On amd64 build locally:

```yaml
builder:
  arch:
    - amd64
  remote:
    host: ssh://docker@docker-builder
```

Build amd64 on local:

```yaml
builder:
  arch:
    - amd64
```

Use docker driver, building for local arch:

```yaml
builder:
  driver: docker
```

lib/kamal/cli/build.rb

@@ -66,7 +66,7 @@ class Kamal::Cli::Build < Kamal::Cli::Base
 
   desc "create", "Create a build setup"
   def create
-    if (remote_host = KAMAL.config.builder.remote_host)
+    if (remote_host = KAMAL.config.builder.remote)
       connect_to_remote_host(remote_host)
     end
 

lib/kamal/commands/builder.rb

@@ -2,7 +2,7 @@ require "active_support/core_ext/string/filters"
 
 class Kamal::Commands::Builder < Kamal::Commands::Base
   delegate :create, :remove, :push, :clean, :pull, :info, :buildx_inspect, :validate_image, :first_mirror, to: :target
-  delegate :multiarch?, :local?, :remote?, to: "config.builder"
+  delegate :local?, :remote?, to: "config.builder"
 
   include Clone
 

lib/kamal/commands/builder/base.rb

@@ -5,8 +5,8 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
 
   delegate :argumentize, to: Kamal::Utils
   delegate \
-    :args, :secrets, :dockerfile, :target, :local_arch, :remote_arch, :remote_host,
-    :cache_from, :cache_to, :multiarch?, :ssh, :driver, :docker_driver?,
+    :args, :secrets, :dockerfile, :target, :arches, :local_arches, :remote_arches, :remote,
+    :cache_from, :cache_to, :ssh, :driver, :docker_driver?,
     to: :builder_config
 
   def clean
@@ -16,7 +16,7 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
   def push
     docker :build,
       "--push",
-      *platform_options,
+      *platform_options(arches),
       *([ "--builder", builder_name ] unless docker_driver?),
       *build_options,
       build_context
@@ -33,7 +33,7 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
   end
 
   def buildx_inspect
-    docker :buildx, :inspect, builder_name
+    docker :buildx, :inspect, builder_name unless docker_driver?
   end
 
   def build_options
@@ -104,4 +104,8 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
     def context_host(builder_name)
       docker :context, :inspect, builder_name, "--format", ENDPOINT_DOCKER_HOST_INSPECT
     end
+
+    def platform_options(arches)
+      argumentize "--platform", arches.map { |arch| "linux/#{arch}" }.join(",") if arches.any?
+    end
 end

lib/kamal/commands/builder/hybrid.rb

@@ -8,18 +8,14 @@ class Kamal::Commands::Builder::Hybrid < Kamal::Commands::Builder::Remote
 
   private
     def builder_name
-      "kamal-hybrid-#{driver}-#{local_arch}-#{remote_arch}-#{remote_host.gsub(/[^a-z0-9_-]/, "-")}"
+      "kamal-hybrid-#{driver}-#{remote.gsub(/[^a-z0-9_-]/, "-")}"
     end
 
     def create_local_buildx
-      docker :buildx, :create, "--name", builder_name, "--platform", "linux/#{local_arch}", "--driver=#{driver}"
+      docker :buildx, :create, *platform_options(local_arches), "--name", builder_name, "--driver=#{driver}"
     end
 
     def append_remote_buildx
-      docker :buildx, :create, "--append", "--name", builder_name, builder_name, "--platform", "linux/#{remote_arch}"
-    end
-
-    def platform
-      "linux/#{local_arch},linux/#{remote_arch}"
+      docker :buildx, :create, *platform_options(remote_arches), "--append", "--name", builder_name, builder_name
     end
 end

lib/kamal/commands/builder/local.rb

@@ -11,14 +11,4 @@ class Kamal::Commands::Builder::Local < Kamal::Commands::Builder::Base
     def builder_name
       "kamal-local-#{driver}"
     end
-
-    def platform_options
-      if multiarch?
-        if local_arch
-          [ "--platform", "linux/#{local_arch}" ]
-        else
-          [ "--platform", "linux/amd64,linux/arm64" ]
-        end
-      end
-    end
 end

lib/kamal/commands/builder/remote.rb

@@ -17,22 +17,13 @@ class Kamal::Commands::Builder::Remote < Kamal::Commands::Builder::Base
       docker(:buildx, :ls)
   end
 
-  def push
-    docker :build,
-      "--push",
-      *platform_options,
-      "--builder", builder_name,
-      *build_options,
-      build_context
-  end
-
   private
     def builder_name
-      "kamal-remote-#{driver}-#{remote_arch}-#{remote_host.gsub(/[^a-z0-9_-]/, "-")}"
+      "kamal-remote-#{driver}-#{remote.gsub(/[^a-z0-9_-]/, "-")}"
     end
 
     def create_remote_context
-      docker :context, :create, builder_name, "--description", "'#{builder_name} host'", "--docker", "'host=#{remote_host}'"
+      docker :context, :create, builder_name, "--description", "'#{builder_name} host'", "--docker", "'host=#{remote}'"
     end
 
     def remove_remote_context
@@ -40,18 +31,10 @@ class Kamal::Commands::Builder::Remote < Kamal::Commands::Builder::Base
     end
 
     def create_buildx
-      docker :buildx, :create, "--name", builder_name, builder_name, "--platform", platform
+      docker :buildx, :create, "--name", builder_name, builder_name
     end
 
     def remove_buildx
       docker :buildx, :rm, builder_name
     end
-
-    def platform_options
-      [ "--platform", platform ]
-    end
-
-    def platform
-      "linux/#{remote_arch}"
-    end
 end

lib/kamal/configuration/builder.rb

@@ -19,16 +19,38 @@ class Kamal::Configuration::Builder
     builder_config
   end
 
-  def multiarch?
-    builder_config["multiarch"] != false
+  def remote
+    builder_config["remote"]
   end
 
-  def local?
-    !!builder_config["local"]
+  def arches
+    Array(builder_config.fetch("arch", default_arch))
+  end
+
+  def local_arches
+    @local_arches ||= if remote
+      uname_m = `uname -m`.strip
+      local_arch = uname_m == "x86_64" ? "amd64" : uname_m
+      arches & [ local_arch ]
+    else
+      arches
+    end
+  end
+
+  def remote_arches
+    @remote_arches ||= if remote
+      arches - local_arches
+    else
+      []
+    end
   end
 
   def remote?
-    !!builder_config["remote"]
+    remote_arches.any?
+  end
+
+  def local?
+    arches.empty? || local_arches.any?
   end
 
   def cached?
@@ -59,18 +81,6 @@ class Kamal::Configuration::Builder
     builder_config.fetch("driver", "docker-container")
   end
 
-  def local_arch
-    builder_config["local"]["arch"] if local?
-  end
-
-  def remote_arch
-    builder_config["remote"]["arch"] if remote?
-  end
-
-  def remote_host
-    builder_config["remote"]["host"] if remote?
-  end
-
   def cache_from
     if cached?
       case builder_config["cache"]["type"]
@@ -120,27 +130,14 @@ class Kamal::Configuration::Builder
 
   private
     def valid?
-      if multiarch?
-        if local?
-          raise ArgumentError, "Invalid builder configuration: local configuration, arch required" unless local_arch
-        end
-
-        if remote?
-          raise ArgumentError, "Invalid builder configuration: remote configuration, arch required" unless remote_arch
-          raise ArgumentError, "Invalid builder configuration: remote configuration, arch required" unless remote_host
-        end
-
       if docker_driver?
-          raise ArgumentError, "Invalid builder configuration: the docker driver does not support multiarch builds"
-        end
-      else
-        raise ArgumentError, "Invalid builder configuration: multiarch must be enabled for local configuration" if local?
-        raise ArgumentError, "Invalid builder configuration: multiarch must be enabled for remote configuration" if remote?
+        raise ArgumentError, "Invalid builder configuration: the `docker` driver does not not support remote builders" if remote
+        raise ArgumentError, "Invalid builder configuration: the `docker` driver does not not support caching" if cached?
+        raise ArgumentError, "Invalid builder configuration: the `docker` driver does not not support multiple arches" if arches.many?
       end
 
       if @options["cache"] && @options["cache"]["type"]
         raise ArgumentError, "Invalid cache type: #{@options["cache"]["type"]}" unless [ "gha", "registry" ].include?(@options["cache"]["type"])
-        raise ArgumentError, "The docker driver does not support caching" if docker_driver?
       end
     end
 
@@ -179,4 +176,8 @@ class Kamal::Configuration::Builder
     def pwd_sha
       Digest::SHA256.hexdigest(Dir.pwd)[0..12]
     end
+
+    def default_arch
+      docker_driver? ? [] : [ "amd64", "arm64" ]
+    end
 end

lib/kamal/configuration/docs/builder.yml

@@ -3,7 +3,7 @@
 # The builder configuration controls how the application is built with `docker build`
 #
 # If no configuration is specified, Kamal will:
-# 1. Create a buildx context called `kamal-<service>-multiarch`
+# 1. Create a buildx context called `kamal-local-docker-container`, using the docker-container driver
 # 2. Use `docker build` to build a multiarch image for linux/amd64,linux/arm64 with that context
 #
 # See https://kamal-deploy.org/docs/configuration/builder-examples/ for more information
@@ -12,41 +12,29 @@
 #
 # Options go under the builder key in the root configuration.
 builder:
-
-  # Multiarch
-  #
-  # Enables multiarch builds, defaults to `true`
-  multiarch: false
-
   # Driver
   #
   # The build driver to use, defaults to `docker-container`
   driver: docker
 
-  # Local configuration
+  # Arch
   #
-  # The build configuration for local builds, only used if multiarch is enabled (the default)
-  #
-  # If there is no remote configuration, by default we build for amd64 and arm64.
-  # If you only want to build for one architecture, you can specify it here.
-  # The docker socket is optional and uses the default docker host socket when not specified
-  local:
-    arch: amd64
-    host: /var/run/docker.sock
+  # The architectures to build for, defaults to `[ amd64, arm64 ]`
+  # Unless you are using the docker driver, when it defaults to the local architecture
+  # You can set an array or just a single value
+  arch:
+    - amd64
 
   # Remote configuration
   #
-  # The build configuration for remote builds, also only used if multiarch is enabled.
-  # The arch is required and can be either amd64 or arm64.
-  remote:
-    arch: arm64
-    host: ssh://docker@docker-builder
+  # If you have a remote builder, you can configure it here
+  remote: ssh://docker@docker-builder
 
   # Builder cache
   #
   # The type must be either 'gha' or 'registry'
   #
-  # The image is only used for registry cache
+  # The image is only used for registry cache. Not compatible with the docker driver
   cache:
     type: registry
     options: mode=max

lib/kamal/configuration/validator.rb

@@ -28,7 +28,11 @@ class Kamal::Configuration::Validator
             elsif key == "hosts"
               validate_servers! value
             elsif example_value.is_a?(Array)
+              if key == "arch"
+                validate_array_of_or_type! value, example_value.first.class
+              else
                 validate_array_of! value, example_value.first.class
+              end
             elsif example_value.is_a?(Hash)
               case key.to_s
               when "options", "args"
@@ -71,6 +75,16 @@ class Kamal::Configuration::Validator
       value.is_a?(String) || value.is_a?(Symbol) || value.is_a?(Numeric) || value.is_a?(TrueClass) || value.is_a?(FalseClass)
     end
 
+    def validate_array_of_or_type!(value, type)
+      if value.is_a?(Array)
+        validate_array_of! value, type
+      else
+        validate_type! value, type
+      end
+    rescue Kamal::ConfigurationError
+      type_error(Array, type)
+    end
+
     def validate_array_of!(array, type)
       validate_type! array, Array
 

test/cli/build_test.rb

@@ -26,7 +26,7 @@ class CliBuildTest < CliTestCase
         assert_match /Cloning repo into build directory/, output
         assert_match /git -C #{Dir.tmpdir}\/kamal-clones\/app-#{pwd_sha} clone #{Dir.pwd}/, output
         assert_match /docker --version && docker buildx version/, output
-        assert_match /docker build --push --platform linux\/amd64,linux\/arm64 --builder kamal-local -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile \. as .*@localhost/, output
+        assert_match /docker build --push --platform linux\/amd64,linux\/arm64 --builder kamal-local-docker-container -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile \. as .*@localhost/, output
       end
     end
   end
@@ -49,7 +49,7 @@ class CliBuildTest < CliTestCase
       SSHKit::Backend::Abstract.any_instance.expects(:execute).with(:git, "-C", build_directory, :submodule, :update, "--init")
 
       SSHKit::Backend::Abstract.any_instance.expects(:execute)
-        .with(:docker, :build, "--push", "--platform", "linux/amd64,linux/arm64", "--builder", "kamal-local", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
+        .with(:docker, :build, "--push", "--platform", "linux/amd64,linux/arm64", "--builder", "kamal-local-docker-container", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
 
       SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
         .with(:git, "-C", anything, :"rev-parse", :HEAD)
@@ -74,7 +74,7 @@ class CliBuildTest < CliTestCase
       assert_no_match /Cloning repo into build directory/, output
       assert_hook_ran "pre-build", output, **hook_variables
       assert_match /docker --version && docker buildx version/, output
-      assert_match /docker build --push --platform linux\/amd64,linux\/arm64 --builder kamal-local -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile . as .*@localhost/, output
+      assert_match /docker build --push --platform linux\/amd64,linux\/arm64 --builder kamal-local-docker-container -t dhh\/app:999 -t dhh\/app:latest --label service="app" --file Dockerfile . as .*@localhost/, output
     end
   end
 
@@ -120,10 +120,10 @@ class CliBuildTest < CliTestCase
         .with(:docker, "--version", "&&", :docker, :buildx, "version")
 
       SSHKit::Backend::Abstract.any_instance.expects(:execute)
-        .with(:docker, :buildx, :create, "--name", "kamal-local", "--driver=docker-container")
+        .with(:docker, :buildx, :create, "--name", "kamal-local-docker-container", "--driver=docker-container")
 
       SSHKit::Backend::Abstract.any_instance.expects(:execute)
-        .with(:docker, :buildx, :inspect, "kamal-local")
+        .with(:docker, :buildx, :inspect, "kamal-local-docker-container")
         .raises(SSHKit::Command::Failed.new("no builder"))
 
       SSHKit::Backend::Abstract.any_instance.expects(:execute).with { |*args| args.first.start_with?("git") }
@@ -137,7 +137,7 @@ class CliBuildTest < CliTestCase
         .returns("")
 
       SSHKit::Backend::Abstract.any_instance.expects(:execute)
-        .with(:docker, :build, "--push", "--platform", "linux/amd64,linux/arm64", "--builder", "kamal-local", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
+        .with(:docker, :build, "--push", "--platform", "linux/amd64,linux/arm64", "--builder", "kamal-local-docker-container", "-t", "dhh/app:999", "-t", "dhh/app:latest", "--label", "service=\"app\"", "--file", "Dockerfile", ".")
 
       run_command("push").tap do |output|
         assert_match /WARN Missing compatible builder, so creating a new one first/, output
@@ -203,23 +203,23 @@ class CliBuildTest < CliTestCase
 
   test "create" do
     run_command("create").tap do |output|
-      assert_match /docker buildx create --name kamal-local --driver=docker-container/, output
+      assert_match /docker buildx create --name kamal-local-docker-container --driver=docker-container/, output
     end
   end
 
   test "create remote" do
     run_command("create", fixture: :with_remote_builder).tap do |output|
       assert_match "Running /usr/bin/env true on 1.1.1.5", output
-      assert_match "docker context create kamal-remote-amd64-ssh---app-1-1-1-5 --description 'kamal-remote-amd64-ssh---app-1-1-1-5 host' --docker 'host=ssh://app@1.1.1.5'", output
-      assert_match "docker buildx create --name kamal-remote-amd64-ssh---app-1-1-1-5 kamal-remote-amd64-ssh---app-1-1-1-5 --platform linux/amd64", output
+      assert_match "docker context create kamal-remote-docker-container-ssh---app-1-1-1-5 --description 'kamal-remote-docker-container-ssh---app-1-1-1-5 host' --docker 'host=ssh://app@1.1.1.5'", output
+      assert_match "docker buildx create --name kamal-remote-docker-container-ssh---app-1-1-1-5 kamal-remote-docker-container-ssh---app-1-1-1-5", output
     end
   end
 
   test "create remote with custom ports" do
     run_command("create", fixture: :with_remote_builder_and_custom_ports).tap do |output|
       assert_match "Running /usr/bin/env true on 1.1.1.5", output
-      assert_match "docker context create kamal-remote-amd64-ssh---app-1-1-1-5-2122 --description 'kamal-remote-amd64-ssh---app-1-1-1-5-2122 host' --docker 'host=ssh://app@1.1.1.5:2122'", output
-      assert_match "docker buildx create --name kamal-remote-amd64-ssh---app-1-1-1-5-2122 kamal-remote-amd64-ssh---app-1-1-1-5-2122 --platform linux/amd64", output
+      assert_match "docker context create kamal-remote-docker-container-ssh---app-1-1-1-5-2122 --description 'kamal-remote-docker-container-ssh---app-1-1-1-5-2122 host' --docker 'host=ssh://app@1.1.1.5:2122'", output
+      assert_match "docker buildx create --name kamal-remote-docker-container-ssh---app-1-1-1-5-2122 kamal-remote-docker-container-ssh---app-1-1-1-5-2122", output
     end
   end
 

test/cli/cli_test_case.rb

@@ -37,7 +37,7 @@ class CliTestCase < ActiveSupport::TestCase
       SSHKit::Backend::Abstract.any_instance.stubs(:execute)
         .with { |arg1, arg2| arg1 == :rm && arg2 == ".kamal/locks/app/details" }
       SSHKit::Backend::Abstract.any_instance.stubs(:execute)
-        .with(:docker, :buildx, :inspect, "kamal-local")
+        .with(:docker, :buildx, :inspect, "kamal-local-docker-container")
     end
 
     def assert_hook_ran(hook, output, version:, service_version:, hosts:, command:, subcommand: nil, runtime: false)

test/commands/builder_test.rb

@@ -5,51 +5,51 @@ class CommandsBuilderTest < ActiveSupport::TestCase
     @config = { service: "app", image: "dhh/app", registry: { "username" => "dhh", "password" => "secret" }, servers: [ "1.1.1.1" ] }
   end
 
-  test "target multiarch by default" do
+  test "target linux/amd64,linux/arm64 locally by default" do
     builder = new_builder_command(builder: { "cache" => { "type" => "gha" } })
     assert_equal "local", builder.name
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
-  test "target native when multiarch is off" do
-    builder = new_builder_command(builder: { "multiarch" => false })
+  test "target specified arch locally by default" do
+    builder = new_builder_command(builder: { "arch" => [ "amd64" ] })
     assert_equal "local", builder.name
     assert_equal \
-      "docker build --push --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
-  test "target native cached when multiarch is off and cache is set" do
-    builder = new_builder_command(builder: { "multiarch" => false, "cache" => { "type" => "gha" } })
+  test "build with caching" do
+    builder = new_builder_command(builder: { "cache" => { "type" => "gha" } })
     assert_equal "local", builder.name
     assert_equal \
-      "docker build --push --builder kamal-local -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
-  test "target multiarch remote when local and remote is set" do
-    builder = new_builder_command(builder: { "local" => { "arch" => "arm64" }, "remote" => { "arch" => "amd64", "host" => "ssh://app@127.0.0.1" }, "cache" => { "type" => "gha" } })
+  test "hybrid build if remote is set" do
+    builder = new_builder_command(builder: { "remote" => "ssh://app@127.0.0.1", "cache" => { "type" => "gha" } })
     assert_equal "hybrid", builder.name
     assert_equal \
-      "docker build --push --platform linux/arm64,linux/amd64 --builder kamal-hybrid-arm64-amd64-ssh---app-127-0-0-1 -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-hybrid-docker-container-ssh---app-127-0-0-1 -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
-  test "target multiarch local when arch is set" do
-    builder = new_builder_command(builder: { "local" => { "arch" => "amd64" } })
-    assert_equal "local", builder.name
-    assert_equal \
-      "docker build --push --platform linux/amd64 --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile .",
-      builder.push.join(" ")
-  end
-
-  test "target native remote when only remote is set" do
-    builder = new_builder_command(builder: { "remote" => { "arch" => "amd64", "host" => "ssh://app@host" }, "cache" => { "type" => "gha" } })
+  test "target remote when remote set and arch is non local" do
+    builder = new_builder_command(builder: { "arch" => [ "#{remote_arch}" ], "remote" => "ssh://app@host", "cache" => { "type" => "gha" } })
     assert_equal "remote", builder.name
     assert_equal \
-      "docker build --push --platform linux/amd64 --builder kamal-remote-amd64-ssh---app-host -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
+      "docker build --push --platform linux/#{remote_arch} --builder kamal-remote-docker-container-ssh---app-host -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
+      builder.push.join(" ")
+  end
+
+  test "target local when remote set and arch is local" do
+    builder = new_builder_command(builder: { "arch" => [ "#{local_arch}" ], "remote" => "ssh://app@host", "cache" => { "type" => "gha" } })
+    assert_equal "local", builder.name
+    assert_equal \
+      "docker build --push --platform linux/#{local_arch} --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
@@ -93,28 +93,21 @@ class CommandsBuilderTest < ActiveSupport::TestCase
   test "build context" do
     builder = new_builder_command(builder: { "context" => ".." })
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ..",
+      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ..",
       builder.push.join(" ")
   end
 
-  test "native push with build args" do
-    builder = new_builder_command(builder: { "multiarch" => false, "args" => { "a" => 1, "b" => 2 } })
-    assert_equal \
-      "docker build --push --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --build-arg a=\"1\" --build-arg b=\"2\" --file Dockerfile .",
-      builder.push.join(" ")
-  end
-
-  test "multiarch push with build args" do
+  test "push with build args" do
     builder = new_builder_command(builder: { "args" => { "a" => 1, "b" => 2 } })
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --build-arg a=\"1\" --build-arg b=\"2\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --build-arg a=\"1\" --build-arg b=\"2\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
-  test "native push with build secrets" do
-    builder = new_builder_command(builder: { "multiarch" => false, "secrets" => [ "a", "b" ] })
+  test "push with build secrets" do
+    builder = new_builder_command(builder: { "secrets" => [ "a", "b" ] })
     assert_equal \
-      "docker build --push --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --secret id=\"a\" --secret id=\"b\" --file Dockerfile .",
+      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --secret id=\"a\" --secret id=\"b\" --file Dockerfile .",
       builder.push.join(" ")
   end
 
@@ -130,31 +123,10 @@ class CommandsBuilderTest < ActiveSupport::TestCase
     assert_equal "docker inspect -f '{{ .Config.Labels.service }}' dhh/app:123 | grep -x app || (echo \"Image dhh/app:123 is missing the 'service' label\" && exit 1)", new_builder_command.validate_image.join(" ")
   end
 
-  test "multiarch context build" do
+  test "context build" do
     builder = new_builder_command(builder: { "context" => "./foo" })
     assert_equal \
-      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ./foo",
-      builder.push.join(" ")
-  end
-
-  test "native context build" do
-    builder = new_builder_command(builder: { "multiarch" => false, "context" => "./foo" })
-    assert_equal \
-      "docker build --push --builder kamal-local -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ./foo",
-      builder.push.join(" ")
-  end
-
-  test "cached context build" do
-    builder = new_builder_command(builder: { "multiarch" => false, "context" => "./foo", "cache" => { "type" => "gha" } })
-    assert_equal \
-      "docker build --push --builder kamal-local -t dhh/app:123 -t dhh/app:latest --cache-to type=gha --cache-from type=gha --label service=\"app\" --file Dockerfile ./foo",
-      builder.push.join(" ")
-  end
-
-  test "remote context build" do
-    builder = new_builder_command(builder: { "remote" => { "arch" => "amd64", "host" => "ssh://app@host" }, "context" => "./foo" })
-    assert_equal \
-      "docker build --push --platform linux/amd64 --builder kamal-remote-amd64-ssh---app-host -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ./foo",
+      "docker build --push --platform linux/amd64,linux/arm64 --builder kamal-local-docker-container -t dhh/app:123 -t dhh/app:latest --label service=\"app\" --file Dockerfile ./foo",
       builder.push.join(" ")
   end
 
@@ -171,4 +143,12 @@ class CommandsBuilderTest < ActiveSupport::TestCase
     def build_directory
       "#{Dir.tmpdir}/kamal-clones/app/kamal/"
     end
+
+    def local_arch
+      `uname -m`.strip == "x86_64" ? "amd64" : "arm64"
+    end
+
+    def remote_arch
+      `uname -m`.strip == "x86_64" ? "arm64" : "amd64"
+    end
 end

test/configuration/builder_test.rb

@@ -14,45 +14,29 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
     }
   end
 
-  test "multiarch?" do
-    assert_equal true, config.builder.multiarch?
-  end
-
-  test "setting multiarch to false" do
-    @deploy_with_builder_option[:builder] = { "multiarch" => false }
-
-    assert_equal false, config_with_builder_option.builder.multiarch?
-  end
-
   test "local?" do
-    assert_equal false, config.builder.local?
+    assert_equal true, config.builder.local?
   end
 
   test "remote?" do
     assert_equal false, config.builder.remote?
   end
 
-  test "remote_arch" do
-    assert_nil config.builder.remote_arch
-  end
-
-  test "remote_host" do
-    assert_nil config.builder.remote_host
+  test "remote" do
+    assert_nil config.builder.remote
   end
 
   test "setting both local and remote configs" do
     @deploy_with_builder_option[:builder] = {
-      "local" => { "arch" => "arm64" },
-      "remote" => { "arch" => "amd64", "host" => "ssh://root@192.168.0.1" }
+      "arch" => [ "amd64", "arm64" ],
+      "remote" => "ssh://root@192.168.0.1"
     }
 
     assert_equal true, config_with_builder_option.builder.local?
     assert_equal true, config_with_builder_option.builder.remote?
 
-    assert_equal "amd64", config_with_builder_option.builder.remote_arch
-    assert_equal "ssh://root@192.168.0.1", config_with_builder_option.builder.remote_host
-
-    assert_equal "arm64", config_with_builder_option.builder.local_arch
+    assert_equal [ "amd64", "arm64" ], config_with_builder_option.builder.arches
+    assert_equal "ssh://root@192.168.0.1", config_with_builder_option.builder.remote
   end
 
   test "cached?" do

test/configuration/validation_test.rb

@@ -90,10 +90,8 @@ class ConfigurationValidationTest < ActiveSupport::TestCase
 
   test "builder" do
     assert_error "builder: unknown key: foo", builder: { "foo" => "bar" }
-    assert_error "builder/remote: should be a hash", builder: { "remote" => true }
-    assert_error "builder/remote: unknown key: foo", builder: { "remote" => { "foo" => "bar" } }
-    assert_error "builder/local: unknown key: foo", builder: { "local" => { "foo" => "bar" } }
-    assert_error "builder/remote/arch: should be a string", builder: { "remote" => { "arch" => [] } }
+    assert_error "builder/remote: should be a string", builder: { "remote" => { "foo" => "bar" } }
+    assert_error "builder/arch: should be an array or a string", builder: { "arch" => {} }
     assert_error "builder/args: should be a hash", builder: { "args" => [ "foo" ] }
     assert_error "builder/cache/options: should be a string", builder: { "cache" => { "options" => [] } }
   end

test/fixtures/deploy_with_remote_builder.yml

@@ -36,6 +36,5 @@ accessories:
 readiness_delay: 0
 
 builder:
-  remote:
-    arch: amd64
-    host: ssh://app@1.1.1.5
+  arch: <%= `uname -m`.strip == "x86_64" ? "arm64" : "amd64" %>
+  remote: ssh://app@1.1.1.5

test/fixtures/deploy_with_remote_builder_and_custom_ports.yml

@@ -40,6 +40,5 @@ ssh:
   port: 22
 
 builder:
-  remote:
-    arch: amd64
-    host: ssh://app@1.1.1.5:2122
+  arch: <%= `uname -m`.strip == "x86_64" ? "arm64" : "amd64" %>
+  remote: ssh://app@1.1.1.5:2122

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

@@ -23,7 +23,6 @@ registry:
   username: root
   password: root
 builder:
-  multiarch: false
   driver: docker
   args:
     COMMIT_SHA: <%= `git rev-parse HEAD` %>

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

@@ -17,7 +17,6 @@ registry:
   username: root
   password: root
 builder:
-  multiarch: false
   driver: docker
   args:
     COMMIT_SHA: <%= `git rev-parse HEAD` %>

test/integration/main_test.rb

@@ -77,7 +77,7 @@ class MainTest < IntegrationTest
     assert_equal "app-#{version}", config[:service_with_version]
     assert_equal [], config[:volume_args]
     assert_equal({ user: "root", port: 22, keepalive: true, keepalive_interval: 30, log_level: :fatal }, config[:ssh_options])
-    assert_equal({ "multiarch" => false, "args" => { "COMMIT_SHA" => version } }, config[:builder])
+    assert_equal({ "driver" => "docker", "args" => { "COMMIT_SHA" => version } }, config[:builder])
     assert_equal [ "--log-opt", "max-size=\"10m\"" ], config[:logging]
     assert_equal({ "cmd"=>"wget -qO- http://localhost > /dev/null || exit 1", "interval"=>"1s", "max_attempts"=>3, "port"=>3000, "path"=>"/up", "cord"=>"/tmp/kamal-cord", "log_lines"=>50 }, config[:healthcheck])
   end