The Case for Highly Available CDP and AIA in Azure, Part 1

This is part one of a four-part series on building a highly available, Azure-hosted CDP and AIA architecture for AD CS. If you want the complete picture in a single reference, including a full architecture diagram, see Highly Available CDP and AIA for ADCS Using Azure. This series goes deeper into each stage: the case for doing this at all, storage setup, fronting it with Azure Front Door, and publishing automation with DNS cutover.

TL;DR: Key Takeaways

Chain validation depends on two network operations that most PKI planning underweights: retrieving the issuing CA’s certificate and checking revocation status, both routed through your CDP and AIA locations.
A single on-premises server hosting these locations is a genuine single point of failure, one that affects every relying party’s ability to validate certificates, not just one user or one application.
Distributed organizations and external relying parties raise the urgency, but the underlying risk exists even for centralized, internal-only deployments.
Planning decisions made now determine how much flexibility you have later: your DNS naming approach specifically, since CDP/AIA URLs are permanently embedded in every certificate you issue from this point forward.

Why On-Premises-Only CDP/AIA Doesn’t Scale

Most certificate validation time is spent on network operations, not cryptographic computation: retrieving the CA’s own certificate and checking whether the certificate being validated has been revoked, both requests travel to wherever your CDP and AIA locations are actually hosted.
A single IIS server hosting these locations concentrates risk in one place, if it’s slow, unreachable, or down, every relying party attempting validation is affected simultaneously, this isn’t a degraded-service scenario, it’s often an outright validation failure.
The risk compounds with organizational distribution, multiple offices, remote and hybrid workers, and external partners or customers validating your certificates all depend on the same infrastructure being reachable and performant from wherever they happen to be.
Centralized, single-office organizations have more flexibility here, but the underlying single point of failure doesn’t disappear, it’s simply less consequential day to day, worth weighing against your organization’s actual risk tolerance rather than assuming it doesn’t apply.

What You’re Actually Deciding When You Plan This

Your DNS naming convention, before anything else: the CDP and AIA URLs you choose now get permanently embedded in every certificate you issue from this point forward, an abstracted hostname, covered in depth in our migration and modernization guide, is what gives you room to change backing infrastructure later without breaking already-issued certificates.
Your redundancy and regional requirements, informed by where your relying parties actually are, a single-region Azure deployment may be entirely sufficient for a centralized organization, while a globally distributed one benefits from genuine multi-region redundancy.
Whether existing on-premises infrastructure needs to keep working during the transition, most organizations can’t cut over instantly, plan for a period where old and new publication points coexist.
How you’ll actually validate the new architecture improves things, rather than just relocating the same single point of failure into a cloud environment, this is where the deeper technical planning in the rest of this series matters.

What’s Coming in This Series

Part 2 covers setting up Azure Storage specifically for CDP/AIA hosting, including the counterintuitive decision to serve content over plain HTTP rather than HTTPS.
Part 3 covers fronting that storage with Azure Front Door for genuine high availability, custom domain HTTPS, and a real, easy-to-miss case-sensitivity issue between IIS and Azure Blob Storage.
Part 4 covers automating publication from your CA environment and the actual DNS cutover that puts the new architecture into production.

How Encryption Consulting Can Help

Getting the planning phase right, particularly DNS and URL abstraction decisions, shapes how much flexibility your PKI retains for years afterward, this is worth getting deliberate expert input on before any infrastructure is provisioned.

Encryption Consulting’s PKI Services team supports this directly:

Architecture planning: working through DNS naming, redundancy requirements, and transition planning specific to your organization’s actual relying party distribution.
Migration sequencing: planning a transition that keeps existing certificates validating throughout, not just after cutover.
Requirements assessment, helping you determine whether a single-region or multi-region architecture actually matches your organization’s risk profile.

If you’re planning a move to Azure-hosted CDP and AIA, our PKI Services team can help you plan it correctly from the start.

Conclusion

Before touching any Azure infrastructure, get clear on why you’re doing this and what you’re actually deciding: DNS abstraction, redundancy scope, and transition sequencing. Part 2 of this series picks up with the actual storage account setup.

Planning a highly available CDP/AIA architecture? Talk to our PKI Services team about getting the design right from the start. Encryption Consulting is ISO/IEC 27001:2022 and SOC 2 certified.

FAQ

Why is a single on-premises IIS server a real risk for CDP and AIA? Because certificate chain validation depends on retrieving both the issuing CA’s certificate and its revocation status over the network. If the server hosting those locations is slow, unreachable, or down, validation fails or times out unpredictably for every relying party attempting it, regardless of how healthy the CA itself is.

Do internal-only PKI deployments need a highly available CDP/AIA architecture? Often less urgently than organizations with external relying parties, but the underlying risk, a single point of failure for every certificate validation, doesn’t disappear just because clients are internal. Organizations with a single office and centralized infrastructure have more flexibility here than distributed or externally facing ones.

What should be decided before starting an Azure CDP/AIA migration? Your abstracted DNS naming convention, your redundancy and regional requirements, whether existing on-premises infrastructure needs to keep working during a transition period, and how you’ll validate the new architecture actually improves availability rather than just relocating the same single point of failure.