SSL is only supported on a single server or with custom SSL certificates

lib/kamal/configuration/proxy.rb

@@ -22,6 +22,10 @@ def ssl?
     proxy_config.fetch("ssl", false)
   end
 
+  def custom_ssl_certificate?
+    proxy_config["ssl_certificate_path"].present?
+  end
+
   def hosts
     proxy_config["hosts"] || proxy_config["host"]&.split(",") || []
   end

lib/kamal/configuration/role.rb

@@ -150,8 +150,8 @@ def asset_volume_directory(version = config.version)
   end
 
   def ensure_one_host_for_ssl
-    if running_proxy? && proxy.ssl? && hosts.size > 1
-      raise Kamal::ConfigurationError, "SSL is only supported on a single server, found #{hosts.size} servers for role #{name}"
+    if running_proxy? && proxy.ssl? && hosts.size > 1 && !proxy.custom_ssl_certificate?
+      raise Kamal::ConfigurationError, "SSL is only supported on a single server or with custom SSL certificates, found #{hosts.size} servers for role #{name}"
     end
   end
 

test/configuration_test.rb

@@ -371,7 +371,16 @@ class ConfigurationTest < ActiveSupport::TestCase
       Kamal::Configuration.new(@deploy_with_roles)
     end
 
-    assert_equal "SSL is only supported on a single server, found 2 servers for role workers", exception.message
+    assert_equal "SSL is only supported on a single server or with custom SSL certificates, found 2 servers for role workers", exception.message
+  end
+
+  test "proxy ssl roles with multiple servers and a custom SSL certificate" do
+    @deploy_with_roles[:servers]["workers"]["proxy"] = { "ssl" => true, "host" => "foo.example.com", "ssl_certificate_path" => "/path/to/cert.pem", "ssl_private_key_path" => "/path/to/key.pem" }
+
+    config = Kamal::Configuration.new(@deploy_with_roles)
+
+    assert config.role(:workers).running_proxy?
+    assert config.role(:workers).ssl?
   end
 
   test "two proxy ssl roles with same host" do