RUMM-1744 Collect Kronos telemetry in Internal Monitoring

[ncreated]

What and why?

📦🔬 This PR adds KronosMonitor for collecting internal telemetry on Kronos execution (NTP sync). This is to gather more data and have more observability on #647.

Note: this additional telemetry will only be collected in apps that enable our Internal Monitoring feature, which means our own dogfood 🐶 projects. It won't be collected from customer apps.

How?

KronosMonitor traces 3 phases of Kronos execution:

• overall clock sync,
• DNS resolution,
• UDP connection to each resolved IP.

internal protocol KronosMonitor {
    // MARK: - Clock sync
    func notifySyncStart(from pool: String)
    func notifySyncEnd(serverOffset: TimeInterval?)

    // MARK: - DNS resolution
    func notifyResolveDNS(to addresses: [KronosInternetAddress])

    // MARK: - IP querying
    func notifyStartQuerying(ip address: KronosInternetAddress, numberOfSamples: Int)
    func notifyReceivePacket(from address: KronosInternetAddress, isValidSample: Bool)
    func notifyEndQuerying(ip address: KronosInternetAddress)
}

Additionally, it uses NWConnection to check UDP connection reachability for each resolved IP on port 123. It then aggregates all results (3 Kronos phases + connection checks to all IPs) and reports single telemetry event (Log), e.g.:

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference

[ncreated]

It is to also collect this telemetry from our E2E tests and run full KronosMonitor logic in CI environment.

[buranmert]

lgtm but i left a comment regarding usage of DispatchGroup

[sergiocampama]

I know this is not the scope of this PR, but could there also be a way to disable clock sync in the API/build settings? This might help mitigate this issue in the mean time for our users. The alternative for me would be to fork the repo and do this on my own, but I'd much prefer to stay on the official Cocoapod dependency.

[ncreated]

I know this is not the scope of this PR, but could there also be a way to disable clock sync in the API/build settings? This might help mitigate this issue in the mean time for our users.

Hello @sergiocampama 🙂👋. Unfortunately, while such API / build setting might work for you it won't work for all our users. If an app uses Datadog Distributed Tracing or tracks 1st party RUM resources, disabling NTP will lead to serious and immediate misalignments in client to server spans causing serious issues in data consistency. We totally understand that some apps might be not collecting distributed telemetry but the set of APIs and configuration options we provide must be equally functional for everyone.

This is why we're not considering it as viable solution to mitigate the problem. Instead, the last sequence of actions we took in dd-sdk-ios should move us closer towards finding the root cause of #647 and fixing it. Meantime we stay open to any help from the OSS community on reproducing the issue.

The alternative for me would be to fork the repo and do this on my own, but I'd much prefer to stay on the official Cocoapod dependency.

I wish I could have better answer for you and I clearly understand why this is important for your users. Unfortunately, a tailor-made fork is currently the only option to disable NTP in dd-sdk-ios. It can be easily achieved by not invoking KronosClock.sync {} in our ServerDateProvider.