[Fleet] "registryProxyUrl" is not allowed to be empty

[slhck]

Kibana version: 8.3.2

Elasticsearch version: 8.3.2

Server OS version: Ubuntu Linux 18.04.6

Browser version: Google Chrome 103.0.5060.134

Browser OS version: macOS 11

Original install method (e.g. download page, yum, from source, etc.): Docker images

Describe the bug:

I have a Docker-based ELK stack that runs in different environments (e.g., on-premise or in the cloud).

Depending on whether the server requires a proxy or not, I want to be able to set the proxy variable through environment variables. This works when I specify the variable explicitly, but when it is an empty string, an error is shown.

For example, assuming the Kibana config:

xpack.fleet.registryProxyUrl: "${KIBANA_PROXY_URL}"

When I launch the Docker container in Docker Compose with:

kibana:
  environment:
    KIBANA_PROXY_URL: ${KIBANA_PROXY_URL:-}

The error I get from Kibana is:

Error: [config validation of [xpack.fleet].registryProxyUrl]: "registryProxyUrl" is not allowed to be empty

When I try to pass an empty string, by changing the Kibana config to:

xpack.fleet.registryProxyUrl: "${KIBANA_PROXY_URL:-}"

I get this error instead:

Error: [config validation of [xpack.fleet].registryProxyUrl]: expected URI with scheme [http|https].

This is a bit of a conundrum. It seems it should be possible for this configuration variable to be either one of the following:

• completely unset → no proxy is applied
• empty string → no proxy is applied
• a string with positive length → proxy URL is verified and proxy setting is applied

In particular, looking at how the URL is actually used, this check here would ensure that an empty string causes the URL to be ignored:

https://github.com/elastic/kibana/blob/ba8c339d84c1d26441f049650296ab4072147128/x-pack/plugins/fleet/server/services/epm/registry/requests.ts#L100-L102

Allowing the variable to be empty would make it possible to have the same base configuration but populate it differently depending on the environment.

[slhck]

I realize now that if I set XPACK_FLEET_REGISTRYPROXYURL via an .env file (or not), I can achieve the same thing.

Just wondering if it's intended for the URL to be parsed that strictly. Feel free to close this issue otherwise!

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[kpollich]

This seems like maybe a lapse in the behavior of the Kibana config SDL, or perhaps Fleet's usage of it - https://github.com/elastic/kibana/tree/main/packages/kbn-config-schema.

Fleet defines the registryProxyUrl config value using Kibana's provided .maybe utility here:

https://github.com/elastic/kibana/blob/db882a06d689c94d68ffce66d69e9533c2fb24f6/x-pack/plugins/fleet/server/config.ts#L102

I think we could potentially get around the issue where an explicitly provided empty string is considered invalid by passing something like defaultValue: "" or explore using nullable instead of maybe in our validation schema.

I'll keep this issue open and toss it on the Fleet backlog, as I think it's probably worth improving the ergonomics here. However, since there's a workaround here using the specific environment variable, we'll consider this low priority.

Thanks for filing this, @slhck!