Local-First Software is Easier to Scale

The ti­tle of this post is some­what mis­lead­ing. Local-first soft­ware rarely needs to be scaled at all.

Harper re­cently re­ceived a mas­sive in­crease in both traf­fic and user count. How? By mak­ing it to the front page of Hacker News. If you could­n’t tell by the ex­tent to which I talk about this, I’m thrilled. This amounted to a tremen­dous amount of free ad­ver­tis­ing, if noth­ing else.

I’ve been think­ing a lot about the won­drous ben­e­fits of work­ing at the edge. That’s just one term of many that peo­ple use to de­scribe Harper: “edge-first”. Others in­clude “local-first” or sim­ply “on-device”. They are all just jar­gon for a sim­ple idea: We run all the rel­e­vant gram­mar check­ing code as phys­i­cally close to the users as pos­si­ble. That way, we can serve up sug­ges­tions faster than any­one else. To achieve our goal, we make sure that every­thing is well-op­ti­mized and lean. Harper barely uses any CPU or mem­ory at all.

What does all this mean in the con­text of the re­cent uptick in user ac­qui­si­tion? Imagine, for a mo­ment, we are LanguageTool. Our soft­ware is writ­ten in Java, with ques­tion­able at­ten­dance to the ef­fi­ciency of our code. Since our soft­ware re­quires a big server to run, we have a cer­tain num­ber of servers on standby to han­dle a cer­tain amount of ex­pected load.

If sud­denly the num­ber of re­quests we re­ceived were to dou­ble (as it did for the Chrome ex­ten­sion), we would be big trou­ble. To avoid in­creas­ing the la­tency on re­quests (or drop­ping re­quests all to­gether), we would need to scale up the num­ber of run­ning servers. This not only takes hir­ing an ex­pert in cloud ar­chi­tec­ture, but also ad­di­tional fund­ing to pay the AWS (or what­ever) bill at the end of the month.

Because Harper runs at the edge (no server re­quired), we don’t have to worry about that. In fact, I only no­ticed that our user count had spiked af­ter I vis­ited Hacker News the morn­ing af­ter. No hic­cups at all.

Lots of cloud providers like to brag about be­ing able to scale with their users. I like to brag about not hav­ing to scale at all.