> For the complete documentation index, see [llms.txt](https://docs.digit.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.digit.org/local-governance/v2.7/platform/configure-digit/configuring-digit-services/zuul-service.md).

# Zuul Service

## Overview <a href="#overview" id="overview"></a>

An API Gateway provides a unified interface for a set of microservices so that clients do not need to know about all the details of microservices internals.

Digit uses Zuul as an edge service that proxies requests to multiple back-end services. It provides a unified “front door” to our ecosystem. This allows any browser, mobile app or other user interfaces to consume underlying services.

## Pre-requisites <a href="#pre-requisites" id="pre-requisites"></a>

Before you proceed with the documentation, make sure the following pre-requisites are met -

* *Java 8*
* egov-user service is running
* egov-accesscontrol service is running

## Key Functionalities <a href="#key-functionalities" id="key-functionalities"></a>

* Provides easier API interface to clients
* Can be used to prevent exposing the internal micro-services structure to the outside world.
* Allows to refactor microservices without forcing the clients to refactor consuming logic
* Can centralize cross-cutting concerns like security, monitoring, rate limiting etc

### Zuul Components <a href="#zuul-components" id="zuul-components"></a>

Zuul has mainly four types of filters that enable us to intercept the traffic in different timelines of the request processing for any particular transaction. We can add any number of filters for a particular url pattern.

* pre filters – are invoked before the request is routed.
* post filters – are invoked after the request has been routed.
* route filters – are used to route the request.
* error filters – are invoked when an error occurs while handling the request.

### Zuul Features <a href="#zuul-features" id="zuul-features"></a>

* Microservice authentication and security
* Authorization
* API Routing
* Open APIs using Whitelisting
* RBAC filter
* Logout filter for finance module
* Property module tax calculation filter for fire cess
* Request enrichment filter:
* Addition of co-relation id
* Addition of authenticated user’s userinfo to requestInfo.
* Error filter:
  * Error response formatting
* Validation Filter to check if a tenant of a particular module is enabled or not.
* Multitenancy Validation Filter. Take the tenant id from Req body or Query Param and validate against additional tenant role or primary tenant role.
* DevOps efficiency: API Response time logging and Send notification if it is taking more time.
* Rate Throttling

## Configuration <a href="#configuration" id="configuration"></a>

**Routing Property**

For each service, the below`-`mentioned property has to be added in `routes.properties`

`1-zuul.routes.{serviceName}.path = /{context path of service}/** 2-zuul.routes.{serviceName}.stripPrefix = {true/false} 3-zuul.routes.{serviceName}.url = {service host name}`

**Rate Limiting Property**

For endpoints which requires rate throttling, below mentioned property has to be added in `limiter.properties`

```
-zuul.ratelimit.policy-list.{serviceName}[0].limit={request number limit per refresh interval window}
-zuul.ratelimit.policy-list.{serviceName}[0].quota={request time limit per refresh interval window (in seconds)}
-zuul.ratelimit.policy-list.{serviceName}[0].refresh-interval={refresh interval in seconds}
-zuul.ratelimit.policy-list.{serviceName}[0].type[0]=url={url of API endpoint}
-zuul.ratelimit.policy-list.{serviceName}[0].type[1]={type of throttling eg: user, origin etc.}
```

## Deployment Details <a href="#deployment-details" id="deployment-details"></a>

1. Deploy the latest version of zuul service.
2. Add zuul routing context paths and service hostname in the configuration.

## Integration <a href="#integration" id="integration"></a>

### Integration Scope <a href="#integration-scope" id="integration-scope"></a>

The zuul service is used to act as an API gateway for services that citizens avail of from the ULBs.

### Integration Benefits <a href="#integration-benefits" id="integration-benefits"></a>

* Can perform service-specific business logic without impacting the other module.
* Provides the capability of routing and authorizing users for accessing resources.

### Steps to Integration <a href="#steps-to-integration" id="steps-to-integration"></a>

1. To integrate, a host of zuul modules should be overwritten in the helm chart.


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