Another year, another platform, another infrastructure project that the vendor documentation assures you is "straightforward." Having just completed a failover configuration between two geographically separate Appgate SDP controller regions, I feel compelled to document the journey. Not for applause, but for the next poor soul who inevitably has to untangle the difference between what's theoretically supported and what actually holds up under a simulated outage.
The impetus was, as always, a previous failure. Not with Appgate, per se, but with a different vendor's "high availability" promise that dissolved into a 45-minute outage because the failover mechanism required a manual DNS change the playbook forgot to mention. So this time, the mandate was explicit: automated, DNS-based, with a tolerable RTO. Appgate's model of active/active controllers across regions is conceptually sound, but the devil is in the configuration symphony—or perhaps cacophony.
Here’s what *actually* broke or required serious thought, versus the glossy overview:
* **The DNS Provider API Integration:** The theory is simple: use health checks to flip DNS records from your primary region to your standby. The reality is your corporate DNS provider (in our case, a legacy one not on Appgate's "preferred" list) becomes a critical single point of failure. The built-in health checks are decent for the Appgate service itself, but they don't inherently understand your broader network pathing. We ended up augmenting with external synthetic transactions.
* **Collector Configuration & The "Split-Brain" Paranoia:** Ensuring collectors in both regions are talking to both controller clusters is vital, but the configuration for failover priorities feels fragile. A misstep here doesn't just cause a failover; it can cause sessions to bounce between regions, creating a miserable user experience and log chaos. The UI doesn't make the dependency chain as visible as it should.
* **The Certificate Tangle:** Everyone warns about certificates, and everyone is right. But it's not just the controller certificates for the FQDN. It's the internal mutual TLS between components, and ensuring your failover FQDN is pre-provisioned and trusted everywhere. Let's just say the "regenerate all" button was used more than once, followed by a mandatory coffee break.
And what improved? Surprisingly, the actual cutover event, once the hair-pulling configuration was locked down, was anti-climatic. The DNS TTL game is still a waiting game, but the internal handoff between controllers for existing user sessions was smoother than expected. The distributed database sync held up, though we watched the metrics like hawks.
So, the ultimate contrarian question: does this setup actually inspire confidence, or does it simply replace one set of known risks (a single region dying) with a new, more complex set of risks (orchestration failure, DNS latency, configuration drift)? I'm leaning towards the latter, but with the caveat that the new risks are at least *different* and, arguably, more within our team's control to script and monitor. I wouldn't call it loyalty; I'd call it managed skepticism.
For those who've walked this path:
* What was your definitive source of truth for health? The controller's own status, gateway reachability, or something external?
* How are you handling the inevitable configuration drift between the two regions now that they're essentially independent until a failover event?
* And be honest, how many test failovers did you run before you trusted it? We're at three and I still feel like we need more.
Oh man, the vendor doc "straightforward" guarantee is a red flag every single time. Been there with dashboard and monitoring systems.
Your point about the DNS provider API integration is so key. The health check logic itself can become a single point of failure if you're not careful. We once had a setup where the check was too "clean" - it passed because the service answered, but the app was actually degraded and couldn't handle real user traffic. The failover never triggered.
Have you looked at using a weighted routing policy alongside the failover? Sometimes a gradual shift, even if automated, beats a hard cutover for user experience. Just a thought from a different angle!
What's your tolerable RTO looking like with this setup?
Data doesn't lie, but dashboards sometimes do.
The manual DNS change being omitted from the playbook sounds painfully familiar. It's the kind of gap that only shows up during the real panic of an outage.
I'm curious about the "configuration symphony" you mentioned. Was the biggest friction getting the Appgate controllers themselves to play nice across regions, or was it more about orchestrating the external pieces like DNS and health checks?
Great question. The real friction wasn't the Appgate controllers themselves, honestly. Once you define the admin tokens and API endpoints for the peer relationship, they handle their own state synchronization fairly well. The documentation, while dense, is accurate on that front.
The "symphony" problem was entirely in the external orchestration. You've got at least three independent systems that all need to agree on the state of the world: the health check service (which probes the controllers), the DNS provider's API, and the controllers' own internal health status. Getting them to converge on a single, stable truth without flapping during a transient network blip was 80% of the work. We ended up implementing a delay and a confirmation count in our health check logic - the secondary region had to fail five consecutive checks over 90 seconds before we'd even consider initiating the DNS switch. Otherwise, you're just trading a vendor outage for a self-inflicted, cascading one.
And that's before you even consider the client-side TTLs.
throughput first
Five checks over 90 seconds is still aggressive. Your orchestration logic is costing you runtime in both regions the entire time. That's double the compute cost for your failover insurance.
You didn't mention where your health check service runs. If it's in one of the two regions, you've just built a circular dependency. The thing deciding the failover can be taken out by the same failure.
show me the bill
Great point on the circular dependency - that's a trap I've seen teams fall into before. In our case, the health checks run from a third, neutral region that's part of our core monitoring infrastructure (totally separate from the Appgate deployment). So the failover decision itself is, thankfully, outside the blast radius.
You're absolutely right about the compute cost for the "insurance." That's the trade-off we debated the most. For our specific risk profile - where even a short outage has a massive financial impact - the ongoing double runtime was approved as a justifiable operational expense. But I totally get that for many use cases, it wouldn't be.