MicroservicePremium
martinfowler.com
martinfowler.com
http://highscalability.com/blog/2014/4/8/microservices-not-a...
Building Microservices does have a real premium - you are building a complex platform which needs specialists skills and additional work to make happen.
The payback of that premium comes later, in the ability to then iterate and change the system easily and quickly.
The problem comes when people think they are building an application and not a platform which will support them for the next 5+ years. I try to hammer this point home to our clients who are looking at Microservice architectures.
In my experience that "iterate and change the system easily and quickly" simply doesn't end up being true. That is the bait, but then comes the switch. Once you have a real system, heavily interdependent, the cost of changing things starts to go up greatly, and your ability to cleanly describe a working system becomes challenging. Answering simple management questions like "OK, so if we change X, what could break?"... "We should send out an email to all the teams to ask!" (ugh)
The problem is that for most significant changes to a component -- there are changes to the interface to that component. So you have 'the choice' -- (1) Maintain this interface forever or (2) Ensure all the teams transition off it by X date, via a deprecation system. Both work, and most companies seem to use a mix of both, they strive for (1) until it gets insane, then they do (2) and force everyone to upgrade to X version by Y date.. rinse and repeat.
We are currently doing the "fat binary" cookie cutter system. Our deploy is a single binary that does "all the things". There is a lot to like about this system. Easy to manage and role back. Compile time checking, including additional tools for static analysis, etc. No network overhead on making local calls. You know and can clearly describe 'the system', it isn't in some continuous flux state. Due to compiling time checking and static analysis you can maintain 'one truth' and when you upgrade a component, you can go into all the callers and update them, so you don't have to maintain that old interface. You can scale decently vertically not just horizontally, which at times is a far more efficient way to scale. Overall, it has made us able to move much faster because it gives us a lot of confidence in what we are shipping, and a sense of safety in that we can quickly go back to what we had.
The impression that gives me is that some of the gain from microservices might be from doing all of the things we're used to doing at service boundaries: documenting APIs, sanity-checking requests, logging, monitoring availability/resource usage/other metrics, etc.--the same sort of things any public Web service does knowing it's going to have to deal with funny clients, rising and falling load, and so on.
If all of the stuff it would take to properly maintain another usable customer-facing service sounds too expensive, that may be a sign that this isn't the place to split off a service. But if you find yourself wishing for separate monitoring, a cleaner API, etc. around some part of your system, it becomes more interesting to separate.
(I can also buy that some folks can see organizational benefits, or benefits from isolating hardware or making operations async, but separate ideas.)
I think the biggest anti-pattern is "DRY". This turns a simple rails view into a monstrosity that is used to render every page of a site, or a class into a self-referencing recursing mind-puzzle.
When a codebase starts down the monolithic path, developers will often use the DRY anti-pattern to "shrink" what is actually complexity creep. They will also use another anti-pattern which is using the test coverage percentage as a key metric for deciding what to build/improve.
Both of these are attempts to fix something that is a far bigger problem: excessive, unnecessary coupling in the core design. This is often because (as others have pointed out) of blind adherence to frameworks and framework "best practices".
In my opinion, the most important metrics are coupling, lines of code (the fewer the better) and readability/understandability. Every line of code that you maintain ads a cost to changing/improving the codebase (because someone has to understand it in order to change it).
If you think of code in terms of its consumers, nearly every API is a micro-service. The less magic/faith required by the consumer to use the API, the more effectively it can be used and changed.
The monolith is simply the opposite of the microservice ideal, it is heavily coupled in both development and deployment.
And yes, DRY does often run counter to the development isolation, as you need to balance repeating yourself or sharing code (and reducing isolation).
As these things generally go, any system in contact with the real world will exist somewhere between the monolith and a federation of microservices. My current company, for example, employs 2 distinct codebases, Java and JavaScript, which have 3 and 2 deployments respectively, each in two similar-but-not-the-same environments (in-house and white-label). We could easily split those deployments into twice or 5x the number, we could also join them, this just happens to be where things naturally settled for the time being.
Every module is built with the intent of breaking away later. Disallowing intra-module communication is essential to this. That means no global ORMs or global anything really.
UI (shared client/server codebase), WebAPI (ui access, auth filtering), DataAPI (used from WebAPI), Profile Service (users/auth), Account Service (core data), Image Service (backs upload/resize) and various backing pieces... for me I didn't break things up into too fine grained pieces, but wanted breaks based on type of work and/or data.
It really just depends on your workload.
Maybe it's just hard to write about a new, interesting thing without most people getting the impression you think it's the way (especially developers, who seem eager to declare any new tool the One True Way® and everything else 'legacy').
[1] http://martinfowler.com/articles/microservices.html#AreMicro...
> So we write this with cautious optimism. So far, we've seen enough about the microservice style to feel that it can be a worthwhile road to tread. We can't say for sure where we'll end up, but one of the challenges of software development is that you can only make decisions based on the imperfect information that you currently have to hand
"We've seen many projects use this style in the last few years, and results so far have been positive, so much so that for many of our colleagues this is becoming the default style for building enterprise applications"
"Monolithic applications can be successful, but increasingly people are feeling frustrations with them "
Man, kind of resonates. Things like SOAP arguably trace back to a reasonable impulse followed with too much zeal.
1) If the system is young and the team is small, consider imposing constraints onto the system that remove certain classes of problems entirely. You can later lift these constraints as the team grows. [1]
2) Your ops environment must be capable of multiplexing multiple services onto the same virtual machine. The way you provision and classify machines is affected by this. Services, by their nature, are small and are likely going to be I/O bound. Deploying multiple services onto a single machine is very cost effective.
3) If you're starting with a monolith, the best early candidates to break off are things like search, graph stuff (eg: Neo4j), recommendations, activity feeds, image processing, and other important but non-critical things. It's a great way to drum up support for this architectural style and/or test how useful it will really be.
4) Unless your engineering team has a polyglot culture (good for you!), be careful about introducing your favorite language when building a new service. Alienating services is a great way for them to rot.
5) I've been asked how to define a service. Should X be one service? Should X be split into two services? A good way to start is to think about data locality. When a "user" is fetched are "friends" almost always queried too? If so, keep them together. The next thing to look at are traffic patterns. Another thought exercise is to ask, "if our startup makes a hard pivot tomorrow, what are we likely going to keep? Users?".
6) Do what makes sense. A small startup with a 5 person team doesn't need 20 "microservices" to maintain. It's an operational burden. Break things away in stages on an as needed basis. I've actually found that keeping around the monolith is a great outlet for rapidly prototyping. Give the monolith a beefy database and an in-memory datastore. When you need to prototype a feature for a week, feed it to the monolith. When it's ready for production, break it off if it makes sense.
7) If your ops environment is underdeveloped, it'll hurt bad. The value of a good ops person cannot be overstated (esp. if you're dealing with rapid growth). They're wizards. Learn everything you can from them.
[1]: I like to impose a constraint that no service is allowed to talk to any other service unless it is: a) customer facing (eg: the website or the mobile api), or b) non-critical and low volume. At first, your services will act as self contained front ends to their databases. Your customer facing applications will stitch together responses from these services (hopefully in parallel). You'll have a clear understanding of how data flows in your system.
This is what PaaSes are for.
If you are a mid/large sized organization it becomes easier to take different approaches... if your single ops guy on a 5-man dev+ops team is overwelmed, and your other main ops person is tied up with coding/architecture then even flushing out such a system is difficult. We're using wildcard DNS to make routing from nginx more straight forward, and deploying each service to 3 dokku-alt servers... which is easier than some of the dynamic provisioning and other pieces behind say coreos/kubernetes.
For that matter, we're keeping our semi-microservices in check, only having a few of them for user-accessed data, and a handful of others for handling work queues.
I've worked on Cloud Foundry and basically it makes deployment a non-issue. Here's how you deploy the service:
cf push the-microservice
cf scale the-microservice -i 100
cf scale the-microservice -m 4G -i 2
cf push the-microservice
I know it's fun to play Dr Frankenstein and hand-roll your own devops system. I've seen systems built out of 3 layers of Jenkins servers, two running Puppet, emitting timestamped RPMs played on fresh VM images. I've seen people use rsync, I've seen them use git, I've seen all manner of clever hacks and they all have the same problem.
You marry this system of deployment and upkeep and now you own it. Forever. By yourself. Then the genius who wrote it leaves, and you're stuck with a system literally nobody else uses.
There's no advantage to writing your own PaaS. Just use one off the shelf.