feat: support custom proxy image repository

[songjiz]

• Allow users to specify custom proxy image repository instead of using default basecamp/kamal-proxy
• Help users in regions where Docker Hub access is restricted (e.g. China) to pull proxy image from cloud vendor repositories
• Move proxy related configurations from configuration to proxy

[AxelTheGerman]

Nice clean up!

I was also looking at proxy configuration options, hoping too override the version with a newer one - see #1252

[dihmeetree]

Would love to see this get introduced/merged! Reason being; Currently Kamal Proxy doesn't have built in support for "Authenticated Origin Pulls" with Cloudflare (requires you to specify a CA Cert, etc), (which is okay.. I get it.. Kamal Proxy is designed to be simple) so I'd most likely fork Kamal Proxy for the time being, add that support, and upload it to Docker Hub or something. Being able to specify my own image would be awesome!

[jethrodaniel]

I also ran into DockerHub's rate-limiting here.

My app's image is hosted on Gitlab's registry, which means that when the server tries to docker pull basecamp/kamal-proxy, it's not authenticated with DockerHub, since the docker login was for a different registry.

I've gotten around the issue by monkey-patching over this in bin/kamal:

diff --git a/bin/kamal b/bin/kamal
index cbe59b9..44f6b98 100755
--- a/bin/kamal
+++ b/bin/kamal
@@ -24,4 +24,14 @@ end
 require "rubygems"
 require "bundler/setup"
 
+#-- PATCH
+require "kamal"
+class Kamal::Configuration
+  def proxy_image
+    # "basecamp/kamal-proxy:#{PROXY_MINIMUM_VERSION}"
+    "registry.gitlab.com/myuser/myapp/kamal-proxy:v0.8.2"
+  end
+end
+#--
+
 load Gem.bin_path("kamal", "kamal")

(and pushing a copy of the kamal-proxy image to my own registry, of course).

Official support for this would be great.