May 21, 2024


“Persevering with our Advancing Reliability weblog collection, which highlights key updates and initiatives associated to enhancing the reliability of the Azure platform and companies, immediately we flip our focus to Azure Energetic Listing (Azure AD). We laid out the core availability rules of Azure AD as a part of this collection again in 2019 so I’ve requested Nadim Abdo, Company Vice President, Engineering, to offer the most recent replace on how our engineering groups are working to make sure the reliability of our identification and entry administration companies which are so important to prospects and companions.”—Mark Russinovich, CTO, Azure


Probably the most important promise of our identification companies is guaranteeing that each person can entry the apps and companies they want with out interruption. We’ve been strengthening this promise to you thru a multi-layered strategy, resulting in our improved promise of 99.99 p.c authentication uptime for Azure Energetic Listing (Azure AD). At present, I’m excited to share a deep dive into usually out there expertise that enables Azure AD to attain even larger ranges of resiliency.

The Azure AD backup authentication service transparently and robotically handles authentications for supported workloads when the first Azure AD service is unavailable. It provides a further layer of resilience on high of the a number of ranges of redundancy in Azure AD. You possibly can consider it as a backup generator or uninterrupted energy provide designed to offer extra fault tolerance whereas staying fully clear and computerized to you. This method operates within the Microsoft cloud however on separate and decorrelated techniques and community paths from the first Azure AD system. Which means that it may possibly proceed to function in case of service, community, or capability points throughout many Azure AD and dependent Azure companies.

What workloads are lined by the service?

This service has been defending Outlook Internet Entry and SharePoint On-line workloads since 2019. Earlier this 12 months we accomplished backup assist for functions working on desktops and cellular gadgets, or “native” apps. All Microsoft native apps together with Workplace 365 and Groups, plus non-Microsoft and customer-owned functions working natively on gadgets at the moment are lined. No particular motion or configuration adjustments are required to obtain the backup authentication protection.

Beginning on the finish of 2021, we’ll start rolling out assist for extra web-based functions. We might be phasing in apps utilizing Open ID Join, beginning with Microsoft internet apps like Groups On-line and Workplace 365, adopted by customer-owned internet apps that use Open ID Join and Safety Assertion Markup Language (SAML).

How does the service work?

When a failure of the Azure AD main service is detected, the backup authentication service robotically engages, permitting the person’s functions to maintain working. As the first service recovers, authentication requests are re-routed again to the first Azure AD service. The backup authentication service operates in two modes:

  • Regular mode: The backup service shops important authentication information throughout regular working circumstances. Profitable authentication responses from Azure AD to dependent apps generate session-specific information that’s securely saved by the backup service for as much as three days. The authentication information is restricted to a device-user-app-resource mixture and represents a snapshot of a profitable authentication at a cut-off date.
  • Outage mode: Any time an authentication request fails unexpectedly, the Azure AD gateway robotically routes it to the backup service. It then authenticates the request, verifies artifacts offered are legitimate (reminiscent of, refresh token, and session cookie), and appears for a strict session match within the beforehand saved information. An authentication response, in line with what the first Azure AD system would have generated, is then despatched to the appliance. Upon restoration, site visitors is dynamically re-routed again to the first Azure AD service.

Diagram showing clients/services like Outlook and Exchange Online accessing tokens – including cached access tokens from the new Backup Auth service

Routing to the backup service is computerized and its authentication responses are in line with these normally coming from the first Azure AD service. Which means that the safety kicks in without having for utility modifications, nor handbook intervention.

Notice that the precedence of the backup authentication service is to maintain person productiveness alive for entry to an app or useful resource the place authentication was not too long ago granted. This occurs to be most of the kind of requests to Azure AD—93 p.c, actually. “New” authentications past the three-day storage window, the place entry was not not too long ago granted on the person’s present gadget, aren’t at the moment supported throughout outages, however most customers entry their most essential functions day by day from a constant gadget.

How are safety insurance policies and entry compliance enforced throughout an outage?

The backup authentication service constantly displays safety occasions which have an effect on person entry to maintain accounts safe, even when these occasions are detected proper earlier than an outage. It makes use of Steady Entry Analysis to make sure the periods which are now not legitimate are revoked instantly. Examples of safety occasions that will trigger the backup service to limit entry throughout an outage embody adjustments to gadget state, account disablement, account deletion, entry being revoked by an admin, or detection of a excessive person threat occasion. Solely as soon as the first authentication service has been restored would a person with a safety occasion be capable to regain entry.

As well as, the backup authentication service enforces Conditional Entry insurance policies. Insurance policies are re-evaluated by the backup service earlier than granting entry throughout an outage to find out which insurance policies apply and whether or not the required controls for relevant insurance policies like multi-factor authentication (MFA) have been glad. If an authentication request is obtained by the backup service and a management like MFA has not been glad, then that authentication could be blocked.

Conditional Entry insurance policies that depend on circumstances reminiscent of person, utility, gadget platform, and IP deal with are enforced utilizing real-time information as detected by the backup authentication service. Nonetheless, sure coverage circumstances (reminiscent of sign-in threat and position membership) can’t be evaluated in real-time, and are evaluated based mostly on resilience settings. Resilience defaults allow Azure AD to soundly maximize productiveness when a situation (reminiscent of group membership) isn’t out there in real-time throughout an outage. The service will consider a coverage assuming that the situation has not modified for the reason that newest entry simply earlier than the outage.

Whereas we extremely suggest prospects to maintain resilience defaults enabled, there could also be some eventualities the place admins would quite block entry throughout an outage when a Conditional Entry situation can’t be evaluated in real-time. For these uncommon instances, directors can disable resilience defaults per coverage inside Conditional Entry. If resilience defaults are disabled by coverage, the backup authentication service won’t serve requests which are topic to real-time coverage circumstances, that means these customers could also be blocked by a main Azure AD outage.

What’s subsequent?

The Azure AD backup authentication service helps customers keep productive within the unlikely state of affairs of an Azure AD main authentication outage. The service supplies one other clear layer of redundancy to our service in a decorrelated Microsoft cloud and community pathways. Sooner or later, we’ll proceed to develop protocol assist, state of affairs assist, and protection past public clouds and we’ll develop the visibility of the service for our superior prospects.

Thanks in your ongoing belief and partnership.


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