That’s a Dilly of a Pickle

by Louis Marascio on September 26, 2008

We’ve all had that moment. You know the feeling, your stomach falls out from under you, your legs go a bit wobbly, or your gut climbs into your throat. It’s an “Oh Shit” moment.

Lot’s of times this happens under relatively benign circumstances. Maybe during a test cycle you realize you forgot some fundamental feature or missed a major requirement. No big deal: just adapt and overcome. However, there are times when those moments are particularly scary.

Building software, especially software that has to integrate with other systems, should always breed a healthy dose of skepticism when diagnosing root cause. What I mean is, there is always a feeling that the problem might not be your own, but in reality, you must always assume that your software is creating the problem, even if it isn’t convenient. Doing otherwise is trying to operate outside of your own sphere of influence: you have no control over the software you integrate with, therefore it is typically a sisyphean task to start there in trying to resolve a problem.

In the many years that I have been building the Metreos/Cisco product that I work on today I have found bugs in other people’s software a mere fraction of the time when compared to my own. It is almost always my fault. I’ve also seen, over and over again, other engineers (some young, some old, I don’t think it is related to your experience level) jump to the immediate conclusion that “it must be xyz in abc’s product” thinking to themselves “there’s no way it could be us”. This is a horrible way to approach problem resolution and root cause identification.

Those really nasty problems almost always happen under the umbrella of a customer found problem. So, coupled with the fact that you’re already facing an “Oh Shit” moment you also have the added stress of knowing that the customer is expecting updates, information, and a fix as soon as possible. An engineer who worked for Metreos’ first customer, and now a good friend, always had something funny to say in these situations:

That’s a dilly of a pickle you’ve got there.

That always made me laugh, but I think the thing that I appreciated about the relationship we had was that he always afforded us the space to work the issue in a logical, diligent, and direct manner. Getting yourself out of hairy spots is much easier when the customer is not being difficult.

So, needless to say, I’ve faced my fair share of pickles over the years. I’ve built up a pretty standard method of analyzing and diagnosing the root cause of the problem. What surprises me is how people try to debug these complicated systems without such an approach. Much of the time you see engineers tossing darts in the dark, hoping to find a solution. The funny thing is, and I’ve seen this first hand as well, is that they might toss one of those darts and see the problem fixed. Unfortunately, without understanding the root cause they never really know whether the real problem is fixed or whether they’ve simply treated the symptom.

Here’s how I typically approach things:

  1. Ensure the problem has been reported properly and is being tracked according to your process. If the problem isn’t being tracked you’re doing the customer a disservice. Make sure it’s logged, has a tracking number, and is visible on whatever process dashboard you might have.
  2. Confirm your understanding of the problem and formulate a set of plausible causes, if possible. It’s sort of amazing how many times you’re initial understanding of the problem is adjacent to the actual experience the customer is having. Take the time to reconfirm, in painful detail, what’s happening and what’s expected to happen.
  3. Analyze available data. If no data is available, ask for data that might already be available by the customer. For example, your standard set of logs that might be turned on in production. Data is critical. Without the data it’s impossible to create a sound hypothesis or confirm environmental events. Many times, people don’t get the data needed because they have some aversion to asking the customer to do work in helping diagnose the situation. If you need the customer to gather network traces from a specific port on a specific switch, tell them so they can do it and get you what you need.
  4. Define a decision tree to isolate root cause. You may choose a positive (rule in) or negative (rule out) approach. Typically the approach you choose is based on your confidence level in plausible root causes you’ve identified. Much of the time, this is less formal than it sounds and is driven from gut feel. If X happens then there is no way the problem is A, but if we see Y then it might be B, etc. The set of possible scenarios and ways those scenarios might be confirmed or refuted is critical because it will push you in a specific direction and tell you where you need to instrument your system or what data you might need to gather.
  5. Gather additional data required to walk your decision tree. Again, don’t be afraid of asking your customer to do work here. They will respect you for taking a disciplined approach to solving their problem.
  6. If you have reached a conclusion based on the decision tree and gathered data, then you have isolated a plausible root cause. Otherwise, go to step 3 and repeat. If you believe you have misunderstood the problem or are no longer able to formulate a decision matrix, go to step 2 and ensure you are not in the weeds. You should end up in a situation that the data has shown you where the problem is, and you are able to confirm the fix works by turning it on or turning it off. Not all problems are as cut and dry, but many are.

Customers respect this approach. In fact, you can make customers love you for following a disciplined, data driven problem solving approach like the one above. A couple of words of wisdom (yes, I said wisdom, does that make me full of myself?):

  1. Make sure they know that you’re in control and are on top of the problem.
  2. Make sure they know what the next steps are.
  3. Don’t be afraid of telling them bad news.
  4. Be honest, clear, and direct with the customer.

There is nothing worse than a waffling, weak engineer on the other end of the line when a major customer problem is in progress.

We had no choice but to follow an approach like this at Metreos, and now at Cisco. The system that we have to diagnose is huge, and problems can be caused by everything from a faulty network element to bad software.

Perhaps the nastiest issue that we had at Metreos was one that was caused by a firewall that would behave differently depending on the order in which specific UDP packets were received. We solved this by having the customer take network traces from various points in the network, making sure we had clear good and bad case examples, and doing some good old fashioned detective work. It was stressful, but quite fun and fulfilling once we were able to show root cause. And best of all, in this specific scenario it wasn’t our bug.

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