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Microservices.md

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MICROSERVICES ARCHITECTURE:

Microservices Architecture:

  • Microservices is an architectural style in which application is structured as a group of individual loosely coupled services.
  • Microservices interact with each other using very light-weight protocol.
  • They are deployed separately.
  • Advantages:
    • Scaling is easier.
    • Easy deployment.
    • Technology usage. (Independent technologies can be used for each service).
    • Faster to develop, and understand.
    • Loosely coupled.
  • Disadvantages:
    • Interprocess communication.
    • Distributed transactions.
    • More resources.
    • Debugging issues.

Monolithic Architecture:

  • One application which has every services packed in it.
  • Advantages:
    • Simple to deploy.
    • Simple to develop.
    • Simple to scale.
  • Disadvantages:
    • Technology dependency. (One technology for all services).
    • Engineering focus.
    • Scaling data layer.
    • Overloaded VM/containers.
    • CI/CD tests (Build and conflicts).
    • Understanding.

Functional Decomposition:

  • A technique where we break down the existing system into smaller different modular services.
  • We decompose the whole application based on the functional areas.

Scale Cube:

  • x-direction: Horizontal Scaling (Adding more instances of similar services).
  • y-direction: Functional decomposition (Keep decomposing the service to certain degree).
  • z-direction: Data partitioning (Processing part of the data by a service instance).

API Gateway:

  • There are three patterns to access data from Microservices:
    1. Direct Call: Client makes direct API calls to all of the microservices and gets the information needed to render the page.
      • Problems:
        • Too many request , Complex JS/Android code to handle
        • Protocol difference of micro services
        • Tigthly coupled client and services
        • Performance issues
        • Scalability issues
    2. API Gateway
    3. BFF
  • An API Gateway is a server that is the single entry point into the system.
  • The API Gateway is responsible for request routing, composition, and protocol translation.
  • All requests from clients first go through the API Gateway.
  • It then routes requests to the appropriate microservice.
  • The API Gateway will often handle a request by invoking multiple microservices and aggregating the results.
  • It can translate between web protocols such as HTTP and WebSocket and web‑unfriendly protocols that are used internally.
  • Advantages:
    • Authentication
    • SSL Termination
    • Load Balancer
    • Insulation
  • Disadvantages:
    • Increased hops
    • Complicated system
  • API Gateway also helps to implement:
    • Caching
    • Managing access quotas
    • API health monitoring
    • API Versioning
    • Chaos Monkey Testing
    • A/B Testing

  • BFF (Backend for frontend):

    • BFF is essentially a variant of the API Gateway pattern.
    • It also provides an additional layer between microservices and clients.
    • But rather than a single point of entry, it introduces multiple gateways for each client.
    • The BFF is tightly focused on a single UI, and just that UI. That allows it to be focused, and will therefore be smaller. image

Service Registry/Discovery:

  • It is a pattern to identify the network addresses of all of the instances of microservices.
  • We use service register for this purpose.
    • Service register is more like a separate system/or a database which contains the list of all of the instances of every microservices and its network addresses.
  • Ways in which service registry can happen:
    1. Self Registry: (The microservices automatically registers themselves to the register).
    2. Third party Registry: (The registry will ask microservices about their address and updates).
  • In discovery we access all of the informations in the registry.

Inter microservices communication:

  • In a monolithic application, components invoke one another via language‑level method or function calls.
  • In contrast, a microservices‑based application is a distributed system running on multiple machines.
  • Each service instance is typically a process.
  • Consequently, microservices must interact using an inter‑process communication (IPC) mechanism.

  • Synchronous inter microservice communication:

    • A synchronous microservice is one in which data moves to and from an endpoint of a service in a blocking interaction.

    • A typical example of a synchronous data exchange is an HTTP request/response interaction. image

    • Advantages:

      • Easy to implement
      • Easy to handle different use cases
      • Realtime

    • Disadvantages:

      • Service Availability
      • Response Time

  • Asynchronous inter microservice communication:

    • An asynchronous microservice is one in which a request to a service and the subsequent response occur independently from each other.

    • The general practice is to use a message broker technology, such as Kafka or RabbitMQ, to act as a go-between for services. image

    • Advantages:

      • Faster APIs
      • Decoupled Services
      • Works even when services are down

    • Disadvantages:

      • Complex design
      • Process latency
      • Monitoring costs

Circuit Breaking:

  • A design pattern which is used when there are services that are interacting with other services.

  • To protect our microservices from an excess of requests, it’s better to interrupt communication between the front-end and the back-end as soon as a recurring fault has been detected in the back-end.

  • Pattern:

    • If a call from one microservice to other microservices fails, increment the number of failed calls by one.
    • If the number of failed calls goes above a certain threshold, open the circuit.
    • If the circuit is open, return with an error or a default response or cached response.
    • If the circuit is open and some wait timeout has passed, half-open the circuit..
    • If the circuit is half-open and the next call fails, open it again.
    • If the circuit is half-open and the next call succeeds, close it.

  • Closed state:

    • This state implies that the service is up and running(properly).
    • Then if the number of error responses from the needed service passes a threshold limit, the circuit breaker will be tripped (ie: goes to the open stage).

  • Open state:

    • In the open state, the circuit breaker will trigger the fallback method.
    • A fallback method will handle the case if the needed service is down.
    • After a considerable time, the circuit breaker will go to half-open state.

  • Half open state:

    • The circuit breaker makes a remote call to the service.
    • If the request fails, the circuit breaker will go to the open stage.
    • If the service gives the proper response, the circuit breaker will go to the closed stage.
    • This state takes place after spending some time in the closed stage.

    image

  • Features:

    • Cached response
    • Fallback mechanism
    • Recover

Service Mesh:

  • Problems faced in inter microservices communication:
    • Load Balance
    • Service discovery
    • Metrics
    • Retries
    • Circuit Breaking
    • Timeout
  • Service mesh: A component which runs along with every microservice deployment and helps to do all of the above problems.
  • It is a sidecar pattern.
    • For every microservice instance, there will be an instance of service mess which is running in that container.
  • It also implements proxy design pattern.
  • In service mesh, there are two major components:
    1. Control Plane
      • The centralized hub or a single hub which acts like a control panel from which we can configure configurations for all of the proxies which are side loaded whith every microservice running in every instance.
    2. Data Plane
      • It is comprised of proxies and all of the requests goes through these proxies.

Deployment Strategies:

  • Deployment goals:
    1. Scalability and throughput
    2. Reliable and available
    3. Isolation
    4. Resource limit
    5. Monitor
    6. Cost effective
  • Patterns:
    1. Multiple Servers Per Host:
      • Advantages:
        • Efficient resource utilization
        • Fast deployment
      • Disadvantages:
        • Poor isolation
        • No resource limit
        • Dependency conflict
    2. Service per VM/container:
      • Advantages:
        • Isolation and secure
        • Manageable
        • Fast(containers only)
        • Autoscaling
      • Disadvantages:
        • Slow (VM only)
        • Not efficient (VM only)
        • Not so secure (containers)
    3. Serverless:
      • Advantages:
        • Focus on code
        • Pay as you go
        • No scaling worries
      • Disadvantages:
        • Runtime support
        • Expensive
        • Vendor lock
        • Debugging pain
        • Stateless and short running process only