How can I add a customized kong plugin into dockerized kong

I tried to do same thing but could not found well-describe answer yet. You can configure simple helloworld plugin as below: (https://github.com/brndmg/kong-plugin-hello-world)

Local 'plugin' directory structure on Docker host:

Then you can mount local /plugins directory and let kong load custom 'helloworld' plugin from /plugins directory

1) using environment variables

$ docker run -d --name kong --network=kong-net \
-e "KONG_DATABASE=cassandra" \
-e "KONG_PG_HOST=kong-database" \ 
-e "KONG_CASSANDRA_CONTACT_POINTS=kong-database" \
**-e "KONG_LUA_PACKAGE_PATH=/plugins/?.lua" \
-e "KONG_CUSTOM_PLUGINS=helloworld" \ ** 
...
-e "KONG_ADMIN_LISTEN=0.0.0.0:8001, 0.0.0.0:8444 ssl" \
**-v "/plugins:/plugins" \**
-p 8080:8000 -p 8443:8443 -p 8001:8001 -p 8444:8444 kong:latest

Then, you can see configured custom plugin on http://[kong-url]:8001/

..
"custom_plugins": [
"helloworld"
],
..

2) Or, you can simple mount your custom kong.conf file which describes plugins you want.

/etc/kong/kong.conf

plugins = bundled,helloworld,jwt-crafter

(It seems that second option is better for latest version of Kong because 'kong_custom_plugin' configuration prints 'deprecation' warning)

For the JWT crafter, https://github.com/foodora/kong-plugin-jwt-crafter it seems that the plugin is not maintained well so that installation using luarocks failed with errors.

$ luarocks install kong-plugin-jwt-crafter
....
kong-plugin-jwt-crafter 1.0-0 depends on lua-resty-jwt ~> 0.1.10-1 (not installed)

Error: Could not satisfy dependency lua-resty-jwt ~> 0.1.10-1: No results matching query were found.

Instead, you can directly to add 'resty-jwt' to official docker image, to resolve dependency, which is not included in official image. and copy "JWT crafter" into "/plugins" directory, and load.

(Inside docker container)

 luarocks install lua-resty-jwt

Hope this helps.