[Fleet]: Error popup under Fleet tab on upgrading Kibana from 7.17.5>8.4.0 having APM integration in Elastic Cloud agent policy

[ghost]

Kibana version: 7.17.5 upgraded to 8.4.0 BC1 Kibana Cloud Environment.

Host OS and Browser version: All, All

Build details:
VERSION: 7.17.5 upgraded to 8.4.0 BC1.
BUILD: 54999
COMMIT: 58f7eaf
ARTIFACT LINK: https://staging.elastic.co/8.4.0-91109cf0/summary-8.4.0.html

Preconditions:

• 7.17.5 upgraded to 8.4.0 BC1 Kibana Cloud Environment should be available.

Steps to reproduce:

1. Login to 7.17.5 Kibana environment.
2. Add Elastic APM integration in Elastic Cloud agent policy.
3. Upgrade the Kibana to 8.4.0 BC1.

Expected Result:

• No Error popup should be there under Fleet tab on upgrading Kibana from 7.17.5>8.4.0 having APM integration in Elastic Cloud agent policy

Screenshot:

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[ghost]

@dikshachauhan-qasource Please review

[dikshachauhan-qasource]

Secondary review is done

[juliaElastic]

From the error message it seems to be introduced by #100413
cc @criamico

[criamico]

I was able to reproduce this issue with the same steps, the error is coming from the api/fleet/agents/setup endpoint:

I think that the problem comes from here:

kibana/x-pack/plugins/fleet/server/services/preconfiguration.ts

Lines 160 to 162 in 6325eb8

	const newFields = {
	defaultDownloadSourceId: defaultDownloadSource.id,
	...fields,

In fact the parameter in AgentPolicy should be download_source_id, not defaultDownloadSourceId, so this is definitely a bug that escaped me while creating the new service. I'll have a fix for it asap as I'll be in PTO the next two weeks.

[ghost]

Hi @criamico
We have revalidated this issue on latest 7.17.5 > 8.4 BC6 Kibana Cloud environment and found it fixed now.

• No Error popup is there under Fleet tab on upgrading Kibana from 7.17.5>8.4.0 having APM integration in Elastic Cloud agent policy

Build details:
VERSION: 7.17.5 upgraded to 8.4.0 BC1.
BUILD: 55395
COMMIT: 1922ab0
ARTIFACT: https://staging.elastic.co/8.4.0-3b80811b/summary-8.4.0.html

Screenshot:

Hence, marking this as QA:Validated.