Allow specifying multiple hosts for kamal proxy via an array

lib/kamal/configuration.rb

@@ -360,7 +360,7 @@ class Kamal::Configuration
     end
 
     def ensure_unique_hosts_for_ssl_roles
-      hosts = roles.select(&:ssl?).map { |role| role.proxy.host }
+      hosts = roles.select(&:ssl?).flat_map { |role| role.proxy.hosts }
       duplicates = hosts.tally.filter_map { |host, count| host if count > 1 }
 
       raise Kamal::ConfigurationError, "Different roles can't share the same host for SSL: #{duplicates.join(", ")}" if duplicates.any?

lib/kamal/configuration/docs/proxy.yml

@@ -28,6 +28,17 @@ proxy:
   # If multiple hosts are needed, these can be specified by comma-separating the hosts.
   host: foo.example.com,bar.example.com
 
+  # Hosts
+  #
+  # The hosts that will be used to serve the app. The proxy will only route requests
+  # to this host to your app.
+  #
+  # If no hosts are set, then all requests will be forwarded, except for matching
+  # requests for other apps deployed on that server that do have a host set.
+  hosts:
+    - foo.example.com
+    - bar.example.com
+
   # App port
   #
   # The port the application container is exposed on.

lib/kamal/configuration/proxy.rb

@@ -22,13 +22,13 @@ class Kamal::Configuration::Proxy
     proxy_config.fetch("ssl", false)
   end
 
-  def host
-    proxy_config["host"]
+  def hosts
+    proxy_config["hosts"] || proxy_config["host"]&.split(",") || []
   end
 
   def deploy_options
     {
-      host: proxy_config["host"],
+      host: hosts.present? ? hosts.join(",") : nil,
       tls: proxy_config["ssl"] ? true : nil,
       "deploy-timeout": seconds_duration(config.deploy_timeout),
       "drain-timeout": seconds_duration(config.drain_timeout),

lib/kamal/configuration/validator/proxy.rb

@@ -3,7 +3,7 @@ class Kamal::Configuration::Validator::Proxy < Kamal::Configuration::Validator
     unless config.nil?
       super
 
-      if config["host"].blank? && config["ssl"]
+      if config["host"].blank? && config["hosts"].blank? && config["ssl"]
         error "Must set a host to enable automatic SSL"
       end
     end

test/commands/app_test.rb

@@ -119,6 +119,22 @@ class CommandsAppTest < ActiveSupport::TestCase
       new_command.deploy(target: "172.1.0.2").join(" ")
   end
 
+  test "deploy with SSL" do
+    @config[:proxy] = { "ssl" => true, "host" => "example.com" }
+
+    assert_equal \
+      "docker exec kamal-proxy kamal-proxy deploy app-web --target \"172.1.0.2:80\" --host \"example.com\" --tls --deploy-timeout \"30s\" --drain-timeout \"30s\" --buffer-requests --buffer-responses --log-request-header \"Cache-Control\" --log-request-header \"Last-Modified\" --log-request-header \"User-Agent\"",
+      new_command.deploy(target: "172.1.0.2").join(" ")
+  end
+
+  test "deploy with SSL targeting multiple hosts" do
+    @config[:proxy] = { "ssl" => true, "hosts" => [ "example.com", "anotherexample.com" ] }
+
+    assert_equal \
+      "docker exec kamal-proxy kamal-proxy deploy app-web --target \"172.1.0.2:80\" --host \"example.com,anotherexample.com\" --tls --deploy-timeout \"30s\" --drain-timeout \"30s\" --buffer-requests --buffer-responses --log-request-header \"Cache-Control\" --log-request-header \"Last-Modified\" --log-request-header \"User-Agent\"",
+      new_command.deploy(target: "172.1.0.2").join(" ")
+  end
+
   test "remove" do
     assert_equal \
       "docker exec kamal-proxy kamal-proxy remove app-web --target \"172.1.0.2:80\"",

test/configuration/proxy_test.rb

@@ -13,6 +13,16 @@ class ConfigurationProxyTest < ActiveSupport::TestCase
     assert_equal true, config.proxy.ssl?
   end
 
+  test "ssl with multiple hosts passed via host" do
+    @deploy[:proxy] = { "ssl" => true, "host" => "example.com,anotherexample.com" }
+    assert_equal true, config.proxy.ssl?
+  end
+
+  test "ssl with multiple hosts passed via hosts" do
+    @deploy[:proxy] = { "ssl" => true, "hosts" => [ "example.com", "anotherexample.com" ] }
+    assert_equal true, config.proxy.ssl?
+  end
+
   test "ssl with no host" do
     @deploy[:proxy] = { "ssl" => true }
     assert_raises(Kamal::ConfigurationError) { config.proxy.ssl? }