Add --proxy-url to the elastic-agent upgrade command

[mbudge]

Hi,

Customers might want to upgrade elastic-agent using the upgrade command on a network using proxies.

Without the --proxy-url command they have to do a manual reinstall if they can't set the proxy.

https://www.elastic.co/guide/en/fleet/current/elastic-agent-cmd-options.html#elastic-agent-upgrade-command

Allowing elastic-agent upgrade do an upgrade of Elastic-agent running in Fleet managed mode would allow customers do an upgrade if there's ever a problem with the Fleet managed upgrade process.

Requirements

• Modify the agent.download section of the elastic-agent.yml to show how a proxy can be configured.
• Add the --proxy-url option to the elastic-agent upgrade command

[cmacknz]

The proxy_url option is supported in the agent.download section of the policy, but looking closer we don't actually document this.

elastic-agent/elastic-agent.yml

Line 157 in 907cfa7

# agent.download:

No reason we can't also support the --proxy-url argument for convenience to avoid having to edit the configuration as well.

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[cmacknz]

For reference, we embed our generic HTTP transport settings configuration into the artfiact configuration structure:

elastic-agent/internal/pkg/agent/application/upgrade/artifact/config.go

Lines 94 to 96 in 4d074b9

	httpcommon.HTTPTransportSettings `config:",inline" yaml:",inline"` // Note: use anonymous struct for json inline
	}

elastic-agent/internal/pkg/agent/application/upgrade/artifact/config.go

Lines 94 to 96 in 4d074b9

	httpcommon.HTTPTransportSettings `config:",inline" yaml:",inline"` // Note: use anonymous struct for json inline
	}

This is what gives us proxy_url in addition to all of the ssl options that exist on our other network connections.

type HTTPClientProxySettings struct {
	// Proxy URL to use for http connections. If the proxy url is configured,
	// it is used for all connection attempts. All proxy related environment
	// variables are ignored.
	URL *ProxyURI `config:"proxy_url" yaml:"proxy_url,omitempty"`

	// Headers configures additional headers that are send to the proxy
	// during CONNECT requests.
	Headers ProxyHeaders `config:"proxy_headers" yaml:"proxy_headers,omitempty"`

	// Disable HTTP proxy support. Configured URLs and environment variables
	// are ignored.
	Disable bool `config:"proxy_disable" yaml:"proxy_disable,omitempty"`
}