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Migrations: The sole scalable fix to tech debt (2018)


The most attention-grabbing migration I ever participated in became once Uber’s migration from Puppet-managed services to a absolutely self-service provisioning mannequin the put any engineer on the corporate might well scuttle up a new service in two clicks. No longer handiest might well they, they did, provisioning more than one services each day by the level the service became once full, and each newly hired engineer spinning up a service from scratch their first day.

What made this migration so attention-grabbing became once the amount. When we started, provisioning a new service took about two weeks of clock time and about two days of engineering time, and we had been falling further on the support of every day. On the time it became once a more-than-correct-a-little worrying, nonetheless it became once moreover a most life like laboratory to learn the potential to flee super-scale application migrations: it became once super ample to circulate attempting to fetch even minute shifts, and long ample that we obtained to experiment with a preference of approaches.

Migrations are both valuable and frustratingly frequent as your codebase ages and your industry grows: most tools and processes handiest reinforce about one remark of magnitude of enhance sooner than turning into ineffective, so rapid enhance makes them one arrangement of existence. This is never always because they’re imperfect processes or unhappy tools, rather the reverse: the truth that something stops working at significantly increased scale is a model that it became once designed because it ought to be to the outdated constraints as an different of being over designed.

Which potential that you swap tools a lot, and your skill emigrate to new application can easily become the defining constraint for your total velocity. Given their importance, we make now not discuss running migrations very commonly; let’s clear up that!

Why migrations subject

Migrations subject because they are frequently the safe on hand avenue to form essential development on technical debt.

Engineers detest technical debt. If there is a straightforward project they are able to in my conception attain to diminish tech debt, they are able to purchase it on themselves. Engineering managers detest technical debt, too. If there is a straightforward project their team can execution in isolation, they are able to rep it scheduled. In mixture, this outcomes in a dynamic the put there is terribly little low-placing fruit to diminish technical debt, and most remaining alternate choices require many teams working collectively to implement them: migrations.

Every migrations targets to invent technical leverage (“your indexes now now not must fit on a single server!”) or decrease technical debt (“your acknowledged writes are assured to persist a grasp failover”) . They recall the awkward territory of lowered immediate contribution this day in alternate for more skill the following day. This makes them controversial to schedule, and as your programs become better, they become more costly.

Lore tells us that Googlers trust a phrase, “Working to face peaceful”, to represent a team whose total skill is consumed in upgrading dependencies and patterns, such that it ought to now not form ahead development on the product/plan they contain. Spending all your time on migrations is ghastly, nonetheless every mid-sized company has a long queue up migrations it ought to now not crew: tantalizing from VMs to containers, rolling out circuit-breaking, tantalizing to the brand new create tool; the list extends with out converse into the sunset.

Migrations are the safe mechanism to successfully arrange technical debt as your organization and code grows. In case you make now not rep good at application and plan migrations, that you can discontinue up languishing in technical debt. (And peaceful must attain one later anyway, or now not it is correct that it is going to potentially be a beefy rewrite.)

Working succesful migrations

The succesful news is that while migrations are onerous, there might be a ravishing identical old playbook that works remarkably well: Derisk, Enable , after which Pause.


The fundamental piece of a migration is derisking it, and to attain so as instant and cheaply as that that you can well trust. Write a map doc and store it with the teams that you trust you studied will trust the toughest time migrating. Iterate. Shop it with teams who trust atypical patterns and edge circumstances. Iterate. Check it in opposition to the following six to 300 and sixty five days of roadmap. Iterate.

After that you can trust superior the map, the following step is to embed into the most tough one or two teams, and work aspect by aspect with those teams to create, evolve and migrate to the brand new plan. Set aside now not birth with the most life like migrations, which can lead to a faux sense of safety.

Efficient derisking is valuable, because every team that endorses a migration is making a raffle on you that that you can well also very well be going to rep this damn part carried out, and now not whisk away them with a migration to an abandoned plan that they must revert. In case you enable one migration in part accomplished, of us shall be exceedingly suspicious of participating within the following.


As soon as that you can trust validated the resolution solves the intended converse, or now not it is time to begin sharpening your tools. Many of us birth migrations by producing tracking tickets for teams to implement, nonetheless or now not it is better to unhurried down and create tooling to programmatically migrate the easy ninety-p.c. This radically reduces the migration’s designate to the broader group, which will enhance their success price and creates more future opportunities emigrate.

As soon as that you can trust dealt with as great of the migration programmatically as that that you can well trust, determine the self-service tooling and documentation that you can well provide to enable of us to form the specified adjustments with out getting stuck. The most good migration tools are incremental and reversible: of us ought to peaceful be ready to directly return to outdated habits if something goes dreadful, and trust the specified expressiveness to derisk their specific migration direction.

Documentation and self-service tooling are merchandise, and thrive below the identical regime: sit down with some teams and explore them practice your instructions, then enhance them. Pick up a one other team, repeat. Spending an further two days intentionally making your documentation super and tools intuitive can put years in super migrations. Enact it!


The leisure piece of a migration is deprecating the legacy plan that you can trust replaced. This requires getting to 100% adoption, and that can be rather tough.

Commence by stopping the bleeding, which is guaranteeing that every newly written code uses the brand new come. That shall be placing in a ratchet in your linters, or updating your documentation and self-service tooling. Here’s consistently the fundamental step, since it turns time into your buddy. As an different of falling on the support of by default, that you can well also very well be now making development by default.

Good ample, now you ought to peaceful birth producing tracking tickets, and a mechanism which pushes migration arrangement to groups that must migrate and to the traditional administration construction. Or now not it is valuable to present wider administration context around migrations because they are the of us who must prioritize the migrations; if a team is never always working on a migration, or now not it is usually because their leadership has now not prioritized it.

At this level that you can well also very well be ravishing shut to full, nonetheless trust the long tail of surprising or unstaffed. Your tool now is terminate it your self. Or now not it is now not necessarily relaxing, nonetheless getting to 100% is going to require the team leading the migration to dig into the nooks and crannies themselves.

My final tip for ending migrations is around recognition. Or now not it is valuable to celebrate migrations while they’re ongoing, nonetheless the massive majority of the celebration and recognition ought to peaceful be reserved for its a success completion. In specific, starting nonetheless now not ending migrations commonly incurs essential technical debt, so your incentives and recognition construction ought to peaceful be cautious to steer clear of perverse incentives.

What trust you ever viewed form migrations simpler? What are about a of the anti-patterns that you can trust skilled?

Due to Ingrid, Jorge and Julia for shaping this put up.

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