The What, Why, and How of a Microservices Architecture

8 Keys to Help You Get Started Today

Hashmap
Hashmap
Jun 7, 2018 · 13 min read

by Jetinder Singh

Image for post
Image for post

For many years now we have been building systems and getting better at it. Several technologies, architectural patterns, and best practices have emerged over those years. Microservices is one of those architectural patterns which has emerged from the world of domain-driven design, continuous delivery, platform and infrastructure automation, scalable systems, polyglot programming and persistence.

What is a Microservices Architecture in a Nutshell?

A microservices architecture takes this same approach and extends it to the loosely coupled services which can be developed, deployed, and maintained independently. Each of these services is responsible for discrete task and can communicate with other services through simple APIs to solve a larger complex business problem.

Key Benefits of a Microservices Architecture

Once developed, these services can also be deployed independently of each other and hence its easy to identify hot services and scale them independent of whole application. Microservices also offer improved fault isolation whereby in the case of an error in one service the whole application doesn’t necessarily stop functioning. When the error is fixed, it can be deployed only for the respective service instead of redeploying an entire application.

Another advantage which a microservices architecture brings to the table is making it easier to choose the technology stack (programming languages, databases, etc.) which is best suited for the required functionality (service) instead of being required to take a more standardized, one-size-fits-all approach.

How Do I Get Started with a Microservices Architecture?

The very next question that comes to mind is “How do I start?” — and — “Is there a standard set of principles which I can follow to help me build a microservices architecture in a better way?”

Well, I’m afraid the answer is “No”.

While that might not sound that promising, there are, however, some common themes which many organizations that have adopted microservices architectures have followed and with which they have ultimately found success. I’ll discuss some of those common themes below.

1. How to Decompose

Identifying business capabilities and corresponding services requires a high level understanding of the business. For example, the business capabilities for an online shopping application might include the following..

● Product Catalog Management

● Inventory Management

● Order Management

● Delivery Management

● User Management

● Product Recommendations

● Product Reviews Management

Once the business capabilities have been identified, the required services can be built corresponding to each of these identified business capabilities.

Each service can be owned by a different team who becomes an expert in that particular domain and an expert in the technologies that are best suited for those particular services. This often leads to more stable API boundaries and more stable teams.

2. Building and Deploying

Once developed, CI/CD pipelines can be setup with any of the available CI servers (Jenkins, TeamCity, Go, etc.) to run the automated test cases and and deploy these service independently to different environments (Integration, QA, Staging, Production, etc).

3. Design the Individual Services Carefully

It is very important to hide any complexity and implementation details of the service and only expose what is needed by the service’s clients. If unnecessary details are exposed, it becomes very difficult to change the service later as there will be alot of painstaking work to determine who is relying on the various parts of the service. Additionally, a great deal of flexibility is lost in being able to deploying the service independently.

The diagram below shows one of the common mistakes in designing microservices:

Image for post
Image for post

As you can see in the diagram, here we are taking a service (Service 1) and storing all of the information needed by the service to a database. When another service (Service 2) is created which needs that same data, we access that data directly from the database.

This approach might seem reasonable and logical in certain instances — maybe it’s easy to access data in a SQL database or write data to a SQL database or maybe the APIs needed by Service 2 are not readily available.

As soon as this approach is adopted, control is immediately lost in determining what is hidden and what is not. Later on, if the schema needs to change, the flexibility to make that change is lost, since you won’t know who is using the database and whether the change will break Service 2 or not.

An alternative approach, and I would submit the right way to tackle this, is below:

Image for post
Image for post

Service 2 should access Service 1 and avoid going directly to the database, therefore preserving utmost flexibility for various schema changes that may be required. Worrying about other parts of the system is eliminated provided you make sure that tests for exposed APIs pass.

As mentioned, choose the protocols for communication between services carefully. For example, if Java RMI is chosen, not only is the user of the API restricted to using a JVM based language, but in addition, the protocol in and of itself is quite brittle because it’s difficult to maintain backward compatibility with the API.

Lastly, when providing client libraries to clients to use the service, think about it carefully, because it’s best to avoid repeating the integration code. If this mistake is made, it can also restrict changes being made in the API if the clients rely on unnecessary details.

4. Decentralize Things

Another way to achieve the same is to have an internal open source model. By taking this approach, the developer who needs changes in a service can check out the code, work on a feature, and submit a PR himself instead of waiting for the service owner to pickup and work on needed changes.

For this model to work properly, the proper technical documentation is needed along with setup instructions and guidance for each service so that it’s easy for anyone to pickup and work on the service.

Another hidden advantage of this approach is that it keeps developers laser focused on writing high quality code as they know that others will be looking at it.

There are also some architectural patterns which can help in decentralizing things. For example, you might have an architecture where the collection of services are communicating via a central message bus.

Image for post
Image for post

This bus handles the routing of messages from different services. Message brokers like RabbitMQ are a good example.

What tends to happen over time is people start putting more and more logic into this central bus and it starts knowing more and more about your domain. As it becomes more intelligent, that can actually become a problem as it becomes difficult to make changes which require coordination across separate dedicated teams.

My general advice for those types of architectures would be to keep them relatively “dumb” and let them just handle the routing. Event based architectures seem to work quite well in those scenarios.

5. Deploy

In Consumer Driven Contracts, each consumer API captures their expectations of the provider in a separate contract. All of these contracts are shared with the provider so that they gain insight into the obligations they must fulfill for each individual client.

Consumer Driven Contracts must pass completely before being deployed and before any changes are made to the API. It also helps the provider to know what services are depending on it and how other services are depending on it.

When it comes to deploying independent microservices, there are two common models.

Multiple Microservices Per Operating System

The downside of this approach is that it limits the ability to change and scale services independently. It also creates difficulty in managing dependencies. For instance, all the services on the same host will have to use same version of Java if they are written in Java. Further, these independent services can produce unwanted side effects for other running services which can be a very difficult problem to reproduce and solve.

One Microservice Per Operating System

With this model, the service is more isolated and hence it’s easier to manage dependencies and scale services independently. But you may ask yourself “Isn’t it expensive”? Well, not really.

The traditional solution for solving this problem is using Hypervisors whereby multiple virtual machines are provisioned on the same host. This solution approach can be cost inefficient as the hypervisor process itself is consuming some resources and, of course, the more VMs that are provisioned, the more resources will be consumed. And that’s where the container model gets good traction and is preferred. Docker is one implementation of that model.

Making Changes to Existing Microservice APIs While In Production

There are different ways to solve this issue.

First, version your API and when changes are required for the API, deploy the new version of the API while still keeping the first version up. The dependent services can then be upgraded at their own pace to use the newer version. Once all of the dependent services are migrated to use the new version of the changed microservice, it can be brought down.

One problem with this approach is that it becomes difficult to maintain the various versions. Any new changes or bug fixes must be done in both the versions.

For this reason, an alternative approach can be considered in which another end point is implemented in the same service when changes are needed. Once the new end point is being fully utilized by all services, then the old end point can be deleted.

The distinct advantage to this approach is that it’s easier to maintain the service as there will always be only one version of the API running.

6. Making Standards

Creating standards such as PayPal’s API Style Guide is always helpful in long run. It’s also important to let others know what an API does and documentation of the API should always be done when creating it. There are tools like Swagger which are very helpful in assisting in development across the entire API lifecycle, from design and documentation, to test and deployment. An ability to create metadata for your API and let users play with it, allows them to know more about it and use it more effectively.

Service Dependencies

Here’s where API Gateways and Service Discovery become very helpful. Implementing an API Gateway becomes a single entry point for all clients, and API Gateways can expose a different API for each client.

The API gateway might also implement security such as verifying that the client is authorized to perform the request. There are some tools like Zookeeper which can be used for Service Discovery (although it was not built for that purpose). There are much more modern tools like etcd and Hashicorp’s Consul which treat Service Discovery as a first class citizen and they are definitely worth looking at for this problem.

7. Failure

What’s critical with a microservices architecture is to ensure that the whole system is not impacted or goes down when there are errors in an individual part of the system.

There are patterns like Bulkhead and Circuits Breaker which can help you achieve better resilency.

Bulkhead

Circuit Breaker

After the timeout expires some calls are allowed by circuit breaker to pass through, and if they succeed the circuit breaker resumes a normal state. For the period the circuit breaker has failed, users can be notified that a certain part of system is broken and the rest of the system can still be used.

Be aware that providing the required level of resiliency for an application can be a multi-dimensional challenge — take a look at Bilgin Ibryam’s post for some great detail “It takes more than a Circuit Breaker to create a resilient application”.

8. Monitoring and Logging

Log Aggregation

Standard tools are available and widely used by various enterprises. ELK Stack is the most frequently used solution, where logging daemon, Logstash, collects and aggregate logs which can be searched via a Kibana dashboard indexed by Elasticsearch.

Stats Aggregation

When one of the downstream services is incapable of handling requests, there should be a way to trigger an alert, and that’s where implementing health check APIs in each service become important — they return information on the health of the system.

A health check client, which could be a monitoring service or a load balancer, invokes the endpoint to check the health of the service instance periodically in a certain time interval. Even if all of the downstream services are healthy, there could still be a downstream communication problem between services. Tools such as Netflix’s Hystrix project enable an ability to identify those types of problems.

One Last Thing

— Start Small —

When you are just starting to develop microservices, start modestly with just one or two services, learn from them, and with time and experience add more.

I wish you the best of success as you travel down this exciting microservices architecture path.


Feel free to share on other channels and be sure and keep up with all new content from Hashmap at https://medium.com/hashmapinc.

Jetinder Singh is Senior Tempus IIoT/IoT Developer at Hashmap working across industries with a group of innovative technologists and domain experts accelerating high value business outcomes for our customers.

HashmapInc

Innovative technologists and domain experts helping…

Hashmap

Written by

Hashmap

Innovative technologists and domain experts accelerating the value of Data, Cloud, IIoT/IoT, and AI/ML for the community and our customers http://hashmapinc.com

HashmapInc

Innovative technologists and domain experts helping accelerate the value of Data, Cloud, IIoT/IoT, and AI/ML for the community and our clients by creating smart, flexible and high-value solutions and service offerings that work across industries. http://hashmapinc.com

Hashmap

Written by

Hashmap

Innovative technologists and domain experts accelerating the value of Data, Cloud, IIoT/IoT, and AI/ML for the community and our customers http://hashmapinc.com

HashmapInc

Innovative technologists and domain experts helping accelerate the value of Data, Cloud, IIoT/IoT, and AI/ML for the community and our clients by creating smart, flexible and high-value solutions and service offerings that work across industries. http://hashmapinc.com

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch

Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore

Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store