"Most of the time he's actually keeping it within a barrier that you can work with." It's a technology race against other global accounting software players and Xero needs to be leading with innovation, says Walker.
Walker's work was recognised last month by American industry magazine CPA Practice Advisor -- Drury was the cover model for the issue -- which listed him in its "40 under 40" roll call of the "best and brightest talent in the accounting profession".
Walker has been at Xero since virtually day one, becoming the software firm's first staff member in May 2006, whereupon he gave himself the CTO title.
Back then Walker was in charge of everything technical, wearing 100 different hats to create the original versions of the software.
"As you grow the company your role is to basically hire your replacement." Until four years ago, Walker was managing teams, overseeing the operational and development sides of the software improvement, but as the organisational structure filled out he was able to take a more defined role.
"Essentially I moved away to build my own team that works on projects that are strategic in nature or they are slightly on the fringe of what you would think of as an accounting system." It was around then that he also moved away from Xero's Wellington HQ to establish the first office in the United States, shifting to San Francisco with wife Catherine, Xero's head of social media.
Not only was it about creating a presence in a market that is key to Xero's success, it was also a way to export the Xero company culture.
"It's very difficult as you grow a global company to keep that culture globally.
"We've got offices all over the place and Rod will tell you one of the things he's most proud of is the fact that he can go to different offices and they're all 'Xeroes'."
Walker had another motivation for heading to North America.
His first years out of university in the late 90s were spent working hard, "doing the quintessential young geek thing of working late nights with the lights off, drinking Red Bull and listening to pounding techno."
It was during this period he met Drury, an "arm waver" at Glazier Systems.
Work got in the way of the classic Kiwi OE, so moving to the United States was a way to deal with the travel bug.
Walker is now based just north of the Flatiron district in downtown Manhattan, in a 10-person office that has something of a start-up vibe.
"Growth is important, size is important.
"You've got to grow to run faster but there is something to be said for small teams." With growth comes scale, the biggest challenge in computing whether you're a global giant like Google or an aspiring start-up, he says.
"What do we look like at a million customers? At five million customers? What's our product architecture going to look like in two years and in five years? What parts of the app need to be completely rewritten because they're five years old and they're not going to scale? What parts of the app are actually looking pretty good? How do we scale the teams so that we're able to run faster?"
In the past 18 months Xero has doubled in size, then doubled again "and that's hard", says Walker.
"It's the same problems as when you start, that's the fascinating thing about it. The same problems but a different scale."
With more than 300,000 customers, and offices around the world it's also about managing the business practices, creating systems that build autonomy "because that allows people to run faster", he says.
"For a period of time last year we had slowed right down which was difficult. Rod was unhappy." It was down to the sheer number of new people joining the company, which almost grinds things to a halt as you bring them up to speed, he says.
Things are now steaming along and Drury is much happier, he adds.
"You're kind of living a case study on how these things work.
"You're just living it and the case study is always changing. It's fascinating."
