Being Just Reliable Enough

One Saturday morning, as I settled in on the couch for a nice do-nothing day of watching college football, my wife reminded me that I had agreed to rake the leaves after putting it off for the last two weekends. Being a good neighbor and not wanting another homeowners’ association (HOA) violation (and it being a bye week for the Longhorns), I grabbed my rake and went outside to work.

fall leaves

There were a lot of leaves. I would say my yard was 100% covered in leaves. I began to rake the leaves and with a modest effort I was able to collect about 90% of the leaves into five piles, which I then transferred into those bags you buy at Home Depot or Costco.

The yard looked infinitely better, but there were still plenty of leaves in the yard. I had the rake, I had the bags, I was already outside, and I was already dirty, so I went to work raking the entire yard again to get the remaining 10% I had missed in the first pass. This took about the same amount of time, but wasn’t nearly as fulfilling. My piles weren’t as impressive, and I was only able to get 90% of the remaining leaves into piles and then into bags, but I had cleared 99% of the leaves.

Still having plenty of daylight and knowing I could do better, I went to work on that last 1%. Now, I don’t know if you know this about leaves, but single leaves can be slippery and evasive. When you don’t have a lot of leaves to clump together to get stuck in the rake it may take two, three, sometimes four passes over the same area to get any good leaf accumulation into your pile. This third pass over the yard was considerably more time consuming, but I was able to get 90% of that remaining 1%. I had now cleared 99.9% of the leaves in my yard.

As I sat back and admired my now mostly leaf-free yard, I could see some individual leaves that had escaped my rake and even some new leaves that had just fallen from the trees. There weren’t too many, but they were there. Wanting to do a good job, I started canvassing the yard on my hands and knees, picking up individual leaves one by one. As you can imagine, this was very tedious and it took much longer to do the whole yard, but I was able to pick up 90% of the remaining 0.1%. I had now cleared 99.99% of the leaves in my yard.

The sun was starting to set and all that was left were mostly little leaf fragments that could only really be picked up by tweezers.

I went inside and asked my wife, “Where are the tweezers?” “Why do you need tweezers to paint the fence?” she asked. “Paint the fence?” I thought. Oh, yeah. I had also agreed to paint the fence today. I told her I hadn’t started on the fence yet and wouldn’t be able to do that this weekend because it was getting late and the Cowboys were playing the next day. She was not happy.

Yes, this story is ridiculous and contrived, but it demonstrates some good points that we apply to how we manage system reliability and new feature velocity at Indeed.

Where did I go wrong? 

It was way before I thought about getting the tweezers. When I started raking, my definition of a successfully raked yard was too vague. I did not have a service level objective (SLO) specifying the percentage of my yard that could be covered in leaves and still be considered well-raked by my clients.

Should I have defined the SLO?

I could have defined the SLO, but I might have based it on what I was capable of achieving. I was capable of picking up bits and pieces of leaves with tweezers until I had a 99.999% leaf-free yard. I could have also gone in the other direction (if it wasn’t a bye week) and determined that raking 90% of the leaves would be sufficient. 

SLOs should be driven by the clients who care about them 

The clients in my story are my HOA and my wife. My HOA cites me when my yard is only 50% raked for an extended period of time. My wife says she is happy when I rake 99% of the leaves once a year. For the SLO, we would take the higher of the two. I could have quit raking leaves after the second pass when I reached 99% and had time to paint the fence (depending on the SLO for the number of coats of paint).

But, I still did a good job, right?

I did, but I far exceeded my undefined SLO of 99% by two 9s, and yet I was not rewarded. Sadly, I was punished, because my wife didn’t care about the work I did on that remaining 1% and was upset that I didn’t have the time to meet my other obligation of painting the fence.

This brings us to the moral of the story:

We need to have the right SLOs and work to exceed them, but not by much. 

At Indeed, when our SLOs describe what our users care about, we avoid the effort of adding unnecessary 9s. We then use that saved effort to deploy more features faster, achieving a balance between reliability and velocity.

About the author

Andrew Ford is a site reliability engineer (SRE) at Indeed, who enjoys solving database reliability and scalability problems. He can be found on the couch from the start of College Gameday to the end of the East Coast game most Saturdays from September to December.

Do you enjoy defining SLOs that your clients care about? Check out SRE openings at Indeed!

Being Just Reliable Enough—cross-posted on Medium.