Welcome!

SDN Journal Authors: Liz McMillan, Yeshim Deniz, Elizabeth White, Pat Romanski, TJ Randall

Related Topics: @CloudExpo, Microservices Expo, @DevOpsSummit

@CloudExpo: Article

Reference Architecture for #Microservices | @CloudExpo #Serverless #DevOps

The goal of microservices is to improve software delivery speed and increase system safety as scale increases

The goal of Microservices is to improve software delivery speed and increase system safety as scale increases. Microservices being modular these are faster to change and enables an evolutionary architecture where systems can change, as the business needs change. Microservices can scale elastically and by being service oriented can enable APIs natively. Microservices also reduce implementation and release cycle time and enables continuous delivery. This paper provides a logical overview of the Microservices Reference Architecture that highlights various sub systems needed to support Microservices deployment and execution.

Introduction
Switch over to Microservices is an hour of need in web application development and delivery and is crucial for the success of Enterprises today.

Of late, enterprises are adopting technologies like analytics, mobility, social media, IoT and smart embedded devices to change customer relationships, internal processes and value propositions. Microservices acts like a bridge between these technologies and provides the building blocks for developing modern distributed enterprise systems to become one of the enablers in the digital transformation journey of the enterprise.

Adoption of Microservices provides the agility, reliability, maintainability, scalability and deploy ability to the enterprises as part of digital transformation process.

There exists many different architecture definition approaches for implementing Microservices across Industry. Many of them are unique and specific to the needs of individual development teams. Many enterprises, without understanding or highlighting the name, have been using an approach towards leveraging APIs that classified as Microservices. This demands a need for designing Reference Architecture to develop and deliver Microservices‑based applications that consumed across the Enterprises.

There exists, numerous articles and blogs on Microservices reference architecture, architecture principles and best practices. This paper summarizes the purpose of Microservices Reference Architecture, drivers for adopting Microservices, Microservices architecture principles and logical view of Microservices Reference Architecture.

Drivers for Microservice Reference Architecture
Microservices are smaller in scope, determined by a focus on domain boundaries and consistent domain modelling, and require less code. In addition, in Monolithic applications, the application components communicate in memory. In the case of Microservices based applications, the communication happens over the network. This leads to software development and deployment becomes more reliable and faster.

With Microservices, each service can scale independently to meet temporary traffic, complete batch processing and other business needs. Improved fault isolation restricts service issues, such as memory leaks or open database connections. The scalability of Microservices complements the flexibility of cloud services improves service and handle more customers simultaneously without interrupting service.

The following diagram represents few key drivers for Enterprises adopting Microservices.

Microservices Architecture Principles
Below are few key architectural principles for Microservices:

Single Responsibility Principle: Each microservice must be responsible for a specific feature or a business functionality or aggregation of cohesive functionality completely.

Granular: Microservice granularity is contained within the intersection of a single functional domain, a single data domain and its immediate dependencies, a self-sufficient packaging and a technology domain.

Domain Driven Design: Domain driven design is an architectural principle in-line with object-oriented approach. It considers the business domain, elements and behaviors and interactions between business domains.

Encapsulation: Each Microservice encapsulates the internal implementation details, so that the external system utilizes the services need not worry about the internals. Encapsulation reduces the complexity and enhances the flexibility of the system.

Loose Coupling: There must be zero coordination necessary for the deployment with other Microservices. The changes in one microsystem should have zero or minimum impact on other services in the eco-system.  

Separation of Concerns: Develop the microservices based on distinct features with zero overlap with other functions. The main objective is to reduce the interaction between services so that they are highly cohesive and loosely coupled. If we separate, the functionality across wrong boundaries will lead tight coupling and increased complexity between services.

Language Neutral: Microservices are composed together to form a complex application, and they do not need to be written using the same programming language. For example, Java might be the correct language for one application, and in others, it might be Python etc.

Hexagonal Architecture: Microservice exposes RESTful APIs for external communication, message broker interface for event notification and database adapters for persistence. This makes hexagonal architecture as a most suitable style for Microservice development.

Sizing of Microservices
It is important that, while designing a Microservice, there is a need to decide on the number and size of individual Microservices. There is no strict rule regarding the optimal size of the Microservice and it depends on the partitioning of the problem space if it is a new development application or splitting the existing monolithic application into individual Microservices.

Also, Microservices cannot be too large or too small. Large services are hard to work with, hard to deploy, and take longer to start and stop. On the other side, when Microservices are too small, the resource cost of deploying and operating such a service overshadows its utility.

Microservice granularity can also be determined based on business needs. Making services too granular, or requiring too many dependencies on other Microservices, can introduce latency.

Microservices allow teams to plan, develop, and deploy features of a system in the cloud without tight coordination. It is therefore, Microservice number and size be dictated by business and technical principles.

Microservices Reference Architecture
Microservices is an architecture style, in which software systems or applications are composed of one or more independent and self-contained services. It is not a product, framework, or platform. It is a strategy for building large distributed systems and are loosely coupled and deployed independently of one another.

The following guidelines to be adapted while designing the services of Microservices Reference Architecture.

  • Lightweight: To facilitate smaller memory footprints and faster start up times
  • Reactive: Applicable for services with concurrent loads or longer response times
  • Stateless: Services scale better and start faster as there is no state to be passivated on shutdown or activated on start up
  • Atomic: helps to do the smallest business unit of work that can be done independently
  • Externalized Configuration: externalize the configurations in the config server, so that it can be maintained in hierarchical structure per environment
  • Consistent: Services should be written in a consistent style as per the coding standards and naming convention guidelines
  • Resilient: Service should handle exceptions arising from technical reasons (connectivity, runtime), and business reasons (invalid inputs) and not crash
  • Reporting: Usage statistics, number of times accessed, average response time, etc. via JMX API
  • Versioned: Support multiple versions for different clients, till all clients migrate to higher versions

Below is the logical view of the Microservices reference architecture.

Fig 2: Microservices Reference Architecture - Logical View

Various components of the reference architecture are described below:

Channels: Channels represents various client side or consumer applications, which will interact with Microservices.

Edge Server: API services or edge services reside on edge server or the API Gateway. Channels interact with the edge services, which decouples the microservices, and keep them channel agnostic.

API gateway is the single entry point for all clients. API Gateway is responsible for aggregating data or, in some cases, acting as a simple routing layer for appropriate services. The API gateway act as a single point of failure. For the coordination between cloud and on premise communication, an API Gateway is used.

The following diagram shows the API gateway interaction patterns

Load Balancer
It is a software based load balancer used for communication between Microservices. Configured for each service for availability, scalability and reliability.

Below diagram show load-balancing scheme.

Decentralized load balancing is the appropriate mechanism for distributing requests between available Microservice instances. Each Microservice can have its own load balancer handling only requests for that Microservice. Client is directly responsible for routing requests to an available Microservice.

API Service: API services need to be exposed either on the edge server or on API Gateway. The Service expose client specific API and can also act as coarse-grained services to orchestrate across multiple Microservices within or across bounded contexts. These services can interact with composite Microservices or directly with core Micro services.

API services can also communicate with the Enterprise Integration Infrastructure (typically ESB/MOM) to access any on premise Enterprise Applications

Composite Service: Composite services orchestrate across multiple core services. These services shall be communicating with the other services using the event-sourcing model or orchestration.

Core services: These services are the basic building blocks for Microservices architecture. These services encapsulate an entity or an aggregate (fine grained) within a given bounded context. Best practice is that, the granularity of the Microservices are always fine grained.

Circuit Breaker: Fault tolerance will ensure that when there is failure, the failed services does not adversely affect the entire system. Without proper mechanisms in place, errors, latencies will trickle up to the calling clients where they will potentially exhaust limited resources. When cascading failures occur, the overall system availability is significantly affected.

The three states of the Circuit Breaker is depicted below,

Closed State
When the service dependency is healthy and no issues detected, the Circuit Breaker is in state of closed. All invocations can pass through the service.

Open State
Circuit Breaker considers the following invocations as failed and factors them in deciding circuit open:

  • Request to the remote service time out
  • Thread pool and bounded task queue used to interact with Service dependency are at 100% capacity
  • Client library used to interact with a service dependency throws an exception

In open state, the circuit breaker reject invocations by either

  • Throwing an exception
  • Returning a fallback output

Half Open State
When the circuit breaker is in Open state, it periodically leaves through one invocation at a configurable interval. If the invocation succeeds, the circuit is closed again.

Cloud Config: It is a single source of configuration data for all other services in a Microservice-based application. Each service can have its configuration in a repository, which centralizes the configuration across all environments. It decouples the configuration from the implementation, which helps to update the configuration without affecting any of the services. Every update on the configuration files in the repository are automatically propagated to the running instances.

Service Discovery: In Microservices application, the dynamic assignment of service instances network locations happens automatically. In addition, the set of service instances changes dynamically because of auto-scaling, failures and upgrades. Consequently, the client code needs to use a service discovery mechanism.

There are two main service discovery patterns: Client-side discovery and Server-side discovery.

  • Client-Side Discovery Pattern: Client is responsible for determining the network locations of available service instances and load balancing requests across them. The client queries a service registry, which is a database of available service instances. The client then uses a load-balancing algorithm to select one of the available service instances and makes a request.
  • Server-Side Discovery Pattern: Client makes the request to a service via a load balancer. The load balancer queries the service registry and routes each request to an available service instance.
  • Service Registry: Service registry is a key part of service discovery. It is a database containing the network locations of service instances. A service registry needs to be highly available and up to date. Clients can cache network locations obtained from the service registry. However, that information eventually becomes out of date and clients become unable to discover service instances.
  • Self-Registration Pattern: Service instance is responsible for registering and deregistering itself with the service registry. In addition, a service instance sends heartbeat requests to prevent its registration from expiring.
  • Third-Party Registration Pattern: In this case, another system component known as the service registrar handles the registration. The service registrar tracks changes to the set of running instances by either polling the deployment environment or subscribing to events. It registers and deregisters the service instances.

Messaging & Events Stream: Lightweight messaging platforms like AMQP shall be used for exchange of messages between microservice within or across bounded contexts or in case of event sourcing used as part of the choreography.

Monitoring: As microservices are distributed and heterogeneous in nature, it is critical to monitor and visualize making sure that software is reliable, available, and performs as expected. Monitoring typically involves collecting metrics from all the applicable systems involved and analyzing/visualizing call graphs. These gets complex as the application complexity (again depends on number microservices and their interactions in a call graph) grows. There are many commercial and open source tools for monitoring microservices.

Distributed Tracing: Distributed tracing helps in how a request traverse through the application, especially when you may not have any insight into the implementation of the microservice you are calling. Tracing tools introduces unique IDs for logging which are consistent between Microservice calls which makes possible to find how a single request travels from one Microservice to the next.

Security: With microservices, security becomes a challenge primarily because no middleware component handles security-based functionality. Instead, each service must handle security on its own, or in some cases, the API layer be made more intelligent to handle the security aspects of the application. Security Frameworks like oAuth2 address the security concern. There are multiple ways of configuring security for microservices; by making API Gateway behave like reverse proxy or by securing each microservice using the security service (backing service like IAM) provided by the PaaS provider.

Backing Services: A PaaS provides services grouped into various categories like database, analytics, security, Data warehouse etc. used by the cloud application. These services expose lightweight protocols (like REST) and consumed by the cloud application by binding. PaaS providers provide consoles (UI based) to manage backing services.

On Premise Integration: API Gateway helps to mediate the communication between cloud and on premise applications. API Services will be used to orchestrate calls that span cloud and on premise by calling the enterprise integration infrastructure for calling any applications on premise.

Infrastructure: Infrastructure has two components; PaaS and IaaS. IaaS is the abstraction onto the hardware and provides on demand resource provisioning. Resources can be scaled out or in based on usage pattern. PaaS is cloud platform residing on top of IaaS. This layer provide the required support for the cloud applications to deploy and run. PaaS provides various runtimes and many backing services required for a cloud application.

Conclusions
Microservices is not a product, framework, or platform. It is a strategy for building large enterprise distributed systems. One of the characteristic of microservice is of loosely coupled and deployed independently of one another. Microservices architecture can offer enterprises many advantages, from independent scalability of diverse application components to faster, easier software development and maintenance. Sizing of the Microservices is very critical for the design of the better services. Open source technology solutions and organizational methods are leading the Microservices market. As a result, Microservices reduce vendor lock-in and eliminate long-term technology commitment, helps to choose the tools need to meet IT and business goals.

In addition, Microservices Reference Architecture need to be developed based on industry‑standard components like Docker containers, and a wide range of languages - Java, PHP, Python, Node.js/JavaScript and Ruby etc. Developed Microservice must expose JavaScript Object Notation (JSON) or Extensible Mark up Language (XML) over the HTTP to provide a REST API. These standards would provide guidelines about how to describe, maintain, and retire Microservices.

Finally, Microservices based System Design is an ongoing story. It is not something that has to done once, and immediately. With the right people, processes, and tools, Microservices can deliver faster development and deployment, easier maintenance, improved scalability, and freedom from long-term technology commitment.

References

  1. "Microservices". martinfowler.com. Retrieved 2017-02-06
  2. S. Newman, Building Microservices - Designing Fine-Grained Systems, O'Reilly, 2015
  3. E. Wolff, Microservices: Flexible Software Architecture, Addison-Wesley, 2016

Acknowledgements

The authors would like to thank Hari Kishan Burle, Raju Alluri of Global Enterprise Architecture

Group of Wipro Technologies for giving the required time and support in many ways in bringing

Up the article as part of Global Enterprise Architecture Practice efforts.

Authors

Dr. Gopala Krishna Behara is a Lead Enterprise Architect in the SCA Practice division of Wipro. He has a total of 21 years of IT experience. Reached at [email protected]

Tirumala Khandrika is a Senior Architect in the SCA Practice division of Wipro. He has a total of 16 years of IT experience. Reached at [email protected]

Sridhar Chalasani is an Architect in the SCA Practice division of Wipro. He has a total of 12 years of IT experience. Reached at [email protected]

Disclaimer

The views expressed in this article/presentation are that of authors and Wipro does not subscribe to the substance, veracity or truthfulness of the said opinion.


DXWorldEXPO LLC, the producer of the world's most influential technology conferences and trade shows has announced the conference tracks for CloudEXPO | DXWorldEXPO 2018 New York.

DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City.

Digital Transformation (DX) is a major focus with the introduction of DXWorldEXPO within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term.

A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throughout enterprises of all sizes.

Register for Full Conference "Gold Pass" ▸ Here (Expo Hall ▸ Here)

Sponsorship Opportunities Here

Speaking Opportunities Here

Sponsorship and Speaking Inquiries: [email protected].

2018 Conference Agenda, Keynotes and 10 Conference Tracks

DXWordEXPO New York 2018 and Cloud Expo New York 2018 agenda present 222 rockstar faculty members, 200 sessions and 22 keynotes and general sessions in 10 distinct conference tracks.

  • Cloud-Native | Serverless
  • DevOpsSummit
  • FinTechEXPO - New York Blockchain Event
  • CloudEXPO - Enterprise Cloud
  • DXWorldEXPO - Digital Transformation (DX)
  • Smart Cities | IoT | IIoT
  • AI | Machine Learning | Cognitive Computing
  • BigData | Analytics
  • The API Enterprise | Mobility | Security
  • Hot Topics | FinTech | WebRTC

Register for Full Conference "Gold Pass" ▸ Here (Expo Hall ▸ Here)

DXWorldEXPO | CloudEXPO 2018 New York cover all of these tools, with the most comprehensive program and with 222 rockstar speakers throughout our industry presenting 22 Keynotes and General Sessions, 200 Breakout Sessions along 10 Tracks, as well as our signature Power Panels. Our Expo Floor brings together the world's leading companies throughout the world of Cloud Computing, DevOps, FinTech, Digital Transformation, and all they entail.

As your enterprise creates a vision and strategy that enables you to create your own unique, long-term success, learning about all the technologies involved is essential. Companies today not only form multi-cloud and hybrid cloud architectures, but create them with built-in cognitive capabilities.

Cloud-Native thinking is now the norm in financial services, manufacturing, telco, healthcare, transportation, energy, media, entertainment, retail and other consumer industries, as well as the public sector.

CloudEXPO is the world's most influential technology event where Cloud Computing was coined over a decade ago and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals.

FinTech Is Now Part of the DXWorldEXPO | CloudEXPO Program!

Financial enterprises in New York City, London, Singapore, and other world financial capitals are embracing a new generation of smart, automated FinTech that eliminates many cumbersome, slow, and expensive intermediate processes from their businesses.

Accordingly, attendees at the upcoming 22nd CloudEXPO | DXWorldEXPO November 11-13, 2018 in New York City will find fresh new content in two new tracks called:

  • FinTechEXPO
  • New York Blockchain Event

which will incorporate FinTech and Blockchain, as well as machine learning, artificial intelligence and deep learning in these two distinct tracks.

Register for Full Conference "Gold Pass" ▸ Here (Expo Hall ▸ Here)

Sponsorship Opportunities Here

Speaking Opportunities Here

Sponsorship and Speaking Inquiries: [email protected].

FinTech brings efficiency as well as the ability to deliver new services and a much improved customer experience throughout the global financial services industry. FinTech is a natural fit with cloud computing, as new services are quickly developed, deployed, and scaled on public, private, and hybrid clouds.

More than US$20 billion in venture capital is being invested in FinTech this year. DXWorldEXPOCloudEXPO are pleased to bring you the latest FinTech developments as an integral part of our program.

DXWorldEXPO | CloudEXPO are accepting speaking submissions for this new track, so please visit Cloud Computing Expo for the latest information or contact us at [email protected]

Register for Full Conference "Gold Pass" ▸ Here (Expo Hall ▸ Here)

Sponsorship Opportunities Here

Speaking Opportunities Here

Sponsorship and Speaking Inquiries: [email protected].

Download Slide Deck ▸ Here

Only DXWorldEXPO | CloudEXPO bring together all this in a single location:

Attend DXWorldEXPO | CloudEXPO. Build your own custom experience. Learn about the world's latest technologies and chart your course to Digital Transformation.

22nd International DXWorldEXPO | CloudEXPO, taking place November 11-13, 2018, in New York City, will feature technical sessions from a rock star conference faculty and the leading industry players in the world.

Register for Full Conference "Gold Pass" ▸ Here (Expo Hall ▸ Here)

Sponsorship Opportunities Here

Speaking Opportunities Here

Sponsorship and Speaking Inquiries: [email protected].

Download Slide Deck: ▸ Here

Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises are using some form of XaaS - software, platform, and infrastructure as a service.

With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.

Every Global 2000 enterprise in the world is now integrating cloud computing in some form into its IT development and operations. Midsize and small businesses are also migrating to the cloud in increasing numbers.

Register for Full Conference "Gold Pass" ▸ Here (Expo Hall ▸ Here)

Sponsorship Opportunities Here

Speaking Opportunities Here

Sponsorship and Speaking Inquiries: [email protected].

Download Slide Deck: ▸ Here

Companies are each developing their unique mix of cloud technologies and services, forming multi-cloud and hybrid cloud architectures and deployments across all major industries. Cloud-driven thinking has become the norm in financial services, manufacturing, telco, healthcare, transportation, energy, media, entertainment, retail and other consumer industries, and the public sector.

Sponsorship Opportunities

DXWorldEXPO | CloudEXPO are the single show where technology buyers and vendors can meet to experience and discus cloud computing and all that it entails. Sponsors of DXWorldEXPO | CloudEXPO will benefit from unmatched branding, profile building and lead generation opportunities through:

  • Featured on-site presentation and ongoing on-demand webcast exposure to a captive audience of industry decision-makers.
  • Showcase exhibition during our new extended dedicated expo hours
  • Breakout Session Priority scheduling for Sponsors that have been guaranteed a 35-minute technical session
  • Online advertising on 4,5 million article pages in SYS-CON's i-Technology Publications
  • Capitalize on our Comprehensive Marketing efforts leading up to the show with print mailings, e-newsletters and extensive online media coverage.
  • Unprecedented PR Coverage: Unmatched editorial coverage on Cloud Computing Journal.
  • Tweetup to over 100,000 plus Twitter followers
  • Press releases sent on major wire services to over 500 industry analysts.

Secrets of Our Most Popular Sponsors and Exhibitors ▸ Here

For more information on sponsorship, exhibit, and keynote opportunities, contact [email protected].

Sponsorship Opportunities Here

Download Slide Deck:Here

Speaking Opportunities

The upcoming 22nd International DXWorldEXPO | CloudEXPO November 11-13, 2018 in New York City, NY announces that its Call For Papers for speaking opportunities is now open.

Secrets of Our Most Popular Faculty Members ▸ Here

Submit your speaking proposal Here or by email [email protected].

Download Slide Deck: ▸ Here

About DXWorldEXPO LLC

DXWorldEXPO LLC is a Lighthouse Point, Florida-based trade show company and the creator of DXWorldEXPODigital Transformation Conference & Expo. The company produces and presents CloudEXPO, DevOpsSummitFinTechEXPO Blockchain Event, the world's most influential conferences and trade shows.

More Stories By Gopala Krishna Behara

Dr. Gopala Krishna Behara is a Senior Enterprise Architect in the Enterprise Architecture & Solutions division of Wipro. He has a total of 16 years of IT experience. He can be reached at [email protected]

More Stories By Sridhar Chalasani

Sridhar Chalasani is an Architect in the Global Enterprise Architecture Practice division of Wipro. He has a total of 12 years of IT experience. He can be reached at [email protected]

More Stories By Tirumala Khandrika

Tirumala Khandrika is a Senior Architect in the Global Enterprise Architecture Practice division of Wipro. He has a total of 16 years of IT experience. He can be reached at [email protected]

CloudEXPO Stories
David Friend is the co-founder and CEO of Wasabi, the hot cloud storage company that delivers fast, low-cost, and reliable cloud storage. Prior to Wasabi, David co-founded Carbonite, one of the world's leading cloud backup companies. A successful tech entrepreneur for more than 30 years, David got his start at ARP Instruments, a manufacturer of synthesizers for rock bands, where he worked with leading musicians of the day like Stevie Wonder, Pete Townsend of The Who, and Led Zeppelin. David has also co-founded five other companies including Computer Pictures Corporation - an early player in computer graphics, Pilot Software - a company that pioneered multidimensional databases for crunching large amounts of customer data for major retail companies, Faxnet - which became the world's largest provider of fax-to-email services, as well as Sonexis - a VoIP conferencing company.
Business professionals no longer wonder if they'll migrate to the cloud; it's now a matter of when. The cloud environment has proved to be a major force in transitioning to an agile business model that enables quick decisions and fast implementation that solidify customer relationships. And when the cloud is combined with the power of cognitive computing, it drives innovation and transformation that achieves astounding competitive advantage.
Machine learning has taken residence at our cities' cores and now we can finally have "smart cities." Cities are a collection of buildings made to provide the structure and safety necessary for people to function, create and survive. Buildings are a pool of ever-changing performance data from large automated systems such as heating and cooling to the people that live and work within them. Through machine learning, buildings can optimize performance, reduce costs, and improve occupant comfort by sharing information within the building and with outside city infrastructure via real time shared cloud capabilities.
Whenever a new technology hits the high points of hype, everyone starts talking about it like it will solve all their business problems. Blockchain is one of those technologies. According to Gartner's latest report on the hype cycle of emerging technologies, blockchain has just passed the peak of their hype cycle curve. If you read the news articles about it, one would think it has taken over the technology world. No disruptive technology is without its challenges and potential impediments that frequently get lost in the hype. The panel will discuss their perspective on what they see as they key challenges and/or impediments to adoption, and how they see those issues could be resolved or mitigated.
Containers and Kubernetes allow for code portability across on-premise VMs, bare metal, or multiple cloud provider environments. Yet, despite this portability promise, developers may include configuration and application definitions that constrain or even eliminate application portability. In this session we'll describe best practices for "configuration as code" in a Kubernetes environment. We will demonstrate how a properly constructed containerized app can be deployed to both Amazon and Azure using the Kublr platform, and how Kubernetes objects, such as persistent volumes, ingress rules, and services, can be used to abstract from the infrastructure.