Sometimes when I talk about customer use cases for software that I’m building, it confuses the people I work with. What does that have to do with engineering? Is my product manager out on leave and I’m standing in?

I’ve found that customer stories connect engineers to the problems we’re solving. When we’re designing a system, we ask ourselves “what if” questions all the time. We need to explore the bounds of the solutions we’re creating, understanding the edge cases. We consider the performance characteristics, scalability requirements and all sorts of other important technical details. Through all this we imagine how the system will interact. It is easier when the software has a human interface, when it interacts with regular people. It is harder, but just as important, when we write software that only interacts with other software systems.

Sometimes the software that we are building can seem quite unrelated from the human world, but it isn’t at all. We then need to understand the bigger system we’re building. At some point, the software has a real-world impact, and we need to understand that, or we can miss creating the positive effects we intend.

On many teams over many years, I’ve had the opportunity to work with other engineers who get this. When it works there’s a rhythm to it, a heartbeat that I stop hearing consciously because it is always there. We talk to customers early and often. We learn about their problems, the other technologies they use, and what is the stuff they understand that we don’t. We start describing our ideas for solutions in their own words. This is not marketing. This influences what we invent. Understanding how to communicate about the thing we’re building changes what we build. We imagine this code we will write, that calls some other code, which causes other software to do a thing, and through all of the systems and layers there is some macro effect, which is important and time critical. Our software may have the capability of doing a thousand things, but we choose the scenarios for performance testing, we decide what is most normal, most routine, and that thing needs to be tied directly to those real effects.

Sometimes we refer to “domain knowledge” if our customers have special expertise, and we need to know that stuff, at least a little bit, so we can relate to our customers (and it’s usually pretty fun to explore someone else’s world a bit). However, the most important thing our customers know, that we need to discover, is what will solve their problems. They don’t know it in their minds — what they describe that they think will solve their problems often doesn’t actually. They know it when they feel it, when they somehow interact with our software and it gives them agency and amplifies their effect in the world.

Our software works when it empowers people to solve their problems and create impact. We can measure that. We can watch that happen. For those of us who have experienced that as software engineers, there’s no going back. We can’t write software any other way.

Customer stories, first hand knowledge from the people whose problems I’m solving spark my imagination, but I’m careful to use those stories with context from quantitative data. I love the product managers who tell me about rapidly expanding markets and how they relate to the use cases embedded in those stories, and research teams who validate whether the story I heard the other day is common across our customers or an edge case. We build software on a set of assumptions. Those assumptions need to be based on reality, and we need to validate early and often whether the thing we’re making is actually going to have a positive effect on reality.

Customer stories are like oxygen to a development team that works like this. Research and design teams who work closely with product managers are like water. When other engineers can’t explain the customer use cases for their software, when they argue about what the solution should be based only on the technical requirements, sometimes I can’t breathe. Then I find the people who are like me, who work like this, and I can hear a heartbeat, I can breathe again, and if feels like this thing we are making just might be awesome.

At Google I/O last week, we presented how to build robust mobile applications for the distributed cloud about building mobile apps in this new world of “serverless development.” When people hear “serverless” sometimes they think we can write code on the server that is just like client-side code, but that’s not really the point.

We have many of the same concerns in developing the code that we always have when we write client-server sofware — we just don’t need to manage servers directly, which drastically reduces operational challenges. In this talk we dive into some specific software development patterns that help us write robust code that scales well.


  • Sarah Allen (me!) I lead the engineering team that works at the intersection of Firebase and Google Cloud on the server side.
  • Judy Tuan introduced me to Firebase over 5 years ago, when she led our team at AngelHack SF (on May 3, 2012) to build an iPhone app that would paint 3D shapes by waving your phone around using the accelerometer. That event happened to be Firebase’s first public launch, and she met Andrew Lee who convinced her to use Firebase in our app. She’s an independent software developer, and also working with Tech Workers Coalition.
  • Jen-Mei Wu is a software architect at Indiegogo, and also volunteers at Liberating Ourselves Locally, a people-of-color-led, gender-diverse, queer and trans inclusive hacker/maker space in East Oakland.

Jen-Mei kicked off the talk by introducing a use case for serverless development based on her work at the maker space, which often works to help non-profits. They are limited in their ability to deploy custom software because they work with small organizations who are staffed by non-technical folk. It doesn’t make sense to set them up with a need to devote resources to updating to the underlying software and operating systems needed to run a web application. With Firebase, the server software is automatically kept up to date with all the needed security patches for all of the required dependencies, it scales up when needed, and scales down to zero cost when not in active use.

The primary use case that motivated the talk from my perspective is for businesses that need to get started quickly, then scale up as usage grows. I found it inspiring to hear about how Firebase supports very small organizations with the same products and infrastructure that auto-scale to a global, distributed network supporting businesses with billions of users.

The concept for this talk was for some real-world developers (Judy and Jen-Mei) to envision an application that would illustrate common patterns in mobile application development, then I recruited a few Firebase engineers to join their open source team and we built the app together.

Severless Patterns

We identified some key needs that are common to mobile applications:

  • People use the app
  • The app stores data
  • The app show the data to people
  • There is some core business logic (“secret sauce”)
  • People interact with each other in some way

The talk details some of the core development patterns:

  • Server-side “special sauce”
  • Authentication & access control
  • Databinding to simplify UI development

The App: Hubbub

Ever go to a conference and feel like you haven’t connected to the people you would have liked to meet? This app seeks to solve that! Using your public GitHub data, we might be able to connect you with other people who share your technical interests. Maybe not, but at least you’ll have lunch with somebody.

You authenticate with GitHub, then the app creates a profile for you by pulling a lot of data from the GitHub API. Your profile might include languages you code in, a list of connections based on your pull request history or the other committers on projects that you have contributed to. Then there’s a list of events, which have a time and place, which people can sign up for. Before the event, people will be placed in groups with a topic they might be interested in. They show up at the appointed time and place, and then to find their assigned group, they open a beacon screen in the app which shows an image that is unique to their group (a pattern of one or more hubbubs with their topic name) and they find each other by holding up their phones.

We built most of the app, enough to really work through the key development patterns, but didn’t have time to hook up the profile generation data collection and implement a good matching algorithm. We ended up using a simple random grouping and were able to test the app at Google I/O for lunch on Friday. Some people showed up and it worked!

You can see the code at:

Many thanks to all the people who joined our open source team to develop the app:

and who helped with the presentation:

  • Virginia Poltrack, graphics
  • Yael Kazaz, public speaking, story-telling coach
  • Puf and Megan, rehearsal feedback
  • Todd Kerpelman our Google I/O mentor
  • Laura Nozay and all of the wonderful Google I/O staff who made the event possible

I built a fake fireplace in celebration of our team shipping Cloud Functions for Firebase. The codename was “hearth” — the product was almost ready for public beta by the time I joined the team, yet I know it was an epic journey to create a long-awaited feature and I felt the milestone deserved dramatic punctuation.

Red brick surrounds a monitor with video of log fire, wooden top has rows of whiskey bottles and a card

If you would like to build your very own fake fireplace, here’s how…

Initial Research

I reached out to our helpful facilities staff to make sure that I understood the constraints of the space. (I didn’t want to buy or create something that would be immediately taken down!) James Miller from facilities investigated some options:

“Since a hearth is technically the flat stone floor or the part outside of the fireplace, putting up just a fireplace and mantel leaves out the most important part, but including it presents a tripping hazard.” He suggested a quick and easy solution would be to temporarily change the display play a 8hr yule log video or on extra computer monitor with some fake foam bricks. He noted that some prop fireplaces which look pretty good in the photos, but are just cardboard. There are more expensive electronic fireplaces, but we can’t have anything that includes heating features similar to a space heater, and he reported “most that I’ve seen online are also missing the most important part… the actual hearth.”

Initially I felt that a literal interpretation of the “hearth” code name was not a critical element. We explored buying a real fake fireplace, but the ones we found were very small and we felt they were very expensive relative to the potential impact. However, his thoughts on the meaning of “hearth” later led to some important design elements. I love being involved in a collaborative creative process!

James suggested that something in a stage prop style would have dramatic effect, perhaps using styrofoam so that it would be light and easy to move, if we needed to shift it in the future around team moves. In brainstorming location, he helped me remember to pick out a spot with an electrical outlet.

Measure Twice, Cut Once

an aisle with people at desks on either side, at the end is a small bookshelf with bottles of alcohol and above that a large monitor on the wallI surreptitiously took a photo of the area, and arrived early one morning with a tape measure to determine its maximum dimension.I then measured the computer monitor I planned to use to determine the minimum internal dimension.

There was actually a third, very important measurement: the internal size of my car, which later became a critical optimization. I designed the fireplace in three pieces, so it could fit into the car, which also made it much lighter and easier to transport. Styrofoam is rather fragile, and the smaller pieces fit easily through doors.

Tools & Supplies

Tools: tape measure, hammer, screw driver, propane torch, safety googles, mask, electric drill, electric sander, garden shears, mat knife, level, steel square

Supplies: small nails, wood, styrofoam panels, gorilla glue, sandpaper, acrylic paint (red, yellow, white, black), gloss latex paint (off-white), sharpie, cardboard

I had never worked with styrofoam before and read that it could be carved with a sharp knife, acetone or a hot knife. If it were a small project, a regular soldering iron would likely have been fine, but I wanted something that would be fast and really liked that the propane torch I found had two different tips as well as an open flame option. The small hand-held propane filled torch is also easier to work with than my electric soldering iron which requires an extension cord.

Construction Details

I tested carving and painting the styrofoam very early, including figuring out how long the paint took to dry. I found that painting the white cracks before painting the red bricks made it come out a bit better. It was also good to test carving to create an effect that looks like mortar.

See key steps in photos

  1. Wooden frame: I uses 1″ thick boards for the frame. Discount Builders in San Francisco has a friendly staff and cut long 12′ or 8′ boards into the lengths I needed. The hearth is a separate component, which is like a hollow box with one side missing, where the missing side is actually attached to the larger frame, so the top can rest on it for stability and is not actually physically attached. I used a level and steel square for an even frame and wood screws.
  2. Top: I used a single 1″ thick board and drilled small holes for pegs to attach the top to the frame in a way that could be easily removed, yet fit snugly. I used garden shears to cut a long wooden dowel into 1″ lengths to create the pegs. I used an electric sander for rounded edges on three sides, and finished with fine sandpaper. I then coated with a few coats of gloss paint (which would have been easier if I had remembered primer!).
  3. Styrofoam: for the large panels I found that using small nails to hold the styrofoam in place made it easier to keep everything steady while gluing it all together. I attached all of the styrofoam panels before carving bricks with the torch. Large cuts were most effective with a mat knife.
  4. Carving the bricks: I found a few inspirational Fireplace images via Google Image Search and drew bricks with a Sharpie, then traced the lines with the torch using the soldering gun tip. Then I went back and made the brick edges a bit irregular and created a few cracks in random bricks. I also used an open flame in areas to create more texture.
  5. Painting the bricks: I mixed acrylic paint with a little dish soap and water, which makes it easier to coat the styrofoam. I noticed that most fireplaces have irregular brick colors, so I varied the colors a bit with yellow and brown highlights, as well as black “sooty” areas.
  6. The inside is painted black with a piece of cardboard as backing.

Additional Resources

I studied sculpture in college, so I had practical experience with wood construction, and learned a bit more from the amazing people who publish about their experience on the web. Here are some links to resources that I found particularly helpful.