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To invoke multiple HTTP APIs in parallel and roll back failed requests in sequence, the developer should use a Scatter-Gather router as a central Saga orchestrator for all API requests with compensating actions for failing routes. A Scatter-Gather router executes multiple routes concurrently and aggregates the results. A Saga orchestrator coordinates a series of actions across different services and handles failures by executing compensating actions. Therefore, using a Scatter-Gather router as a Saga orchestrator allows invoking multiple HTTP APIs in parallel and rolling back any failed requests in sequence. References: https://docs.mulesoft.com/mule-runtime/4.3/scatter-gather-concept https://docs.mulesoft.com/mule-runtime/4.3/saga

When an HTTP request is received and the HTTP Caching policy is applied first, it checks if there is a cached response for that request in Object Store. If there is a cache hit, meaning that a valid cached response exists, then only the HTTP Caching policy is evaluated and the cached response is returned to the caller without invoking the OAuth policy or the API implementation. If there is a cache miss, meaning that no valid cached response exists, then both the HTTP Caching policy and the OAuth policy are evaluated before invoking the API implementation. References:https://docs.mulesoft.com/api-manager/2.x/http-caching-policy#policy-ordering

To log all the errors raised by the VM Connector, the developer needs to add an async logger with the name ‘org.mule.extension.vm’ and the level ‘ERROR’ inside the appenders tag of the log4j2.xml file. This will enable logging all error-level events generated by the VM Connector to the console appender. References:https://docs.mulesoft.com/mule-runtime/4.3/logging-in-mule#configuring-custom-logging-settings

To validate the data before posting to the target system, the developer should add the JSON module dependency and add the validate-schema operation in the flow, configured to reference the schema. The JSON module provides a validate-schema operation that validates a JSON payload against a JSON schema and throws an error if the payload is invalid. References:https://docs.mulesoft.com/json-module/1.1/json-validate-schema

When implementing a synchronous API where the event source is an HTTP Listener, Mule automatically propagates some message attributes between flows via outbound and inbound properties. One of these attributes is correlation ID, which is returned to the caller in the response header by default as MULE_CORRELATION_ID. References: https://docs.mulesoft.com/mule-runtime/4.3/about-mule-message#message-attributes

To invoke Bioinfo System API using its REST Connector, option E should be added to the pom.xml file. This option adds a dependency for Bioinfo System API REST Connector with its group ID, artifact ID, version, classifier, and type. The classifier specifies that it is a REST Connector (raml-client), and the type specifies that it is a Mule plugin (mule-plugin). References:https://docs.mulesoft.com/apikit/4.x/apikit-4-generate-from-rest-api-task#add-the-api-dependency-to-the-pom-file

To test that the payment API is working in production, the developer should create a health check endpoint that listens on a separate port and uses a separate HTTP Listener configuration from the API. This way, the developer can isolate the health check endpoint from the API traffic and avoid affecting the performance or availability of the API. The health check endpoint should return a simple response that indicates the status of the API, such as OK or ERROR. References:https://docs.mulesoft.com/api-functional-monitoring/afm-create-monitor#create-a-monitor

To handle a permanent error response like HTTP:UNAUTHORIZED inside Until Successful, the developer should put the HTTP Request inside a try scope in Unit Successful, and use On Error Continue to catch permanent errors like HTTP UNAUTHORIZED in the error handler. This way, the developer can avoid retrying requests that will always fail due to a permanent error, and reduce latency. On Error Continue allows the flow to continue processing after handling the error. References: https://docs.mulesoft.com/mule-runtime/4.3/until-successful-scope https://docs.mulesoft.com/mule-runtime/4.3/on-error-continue-concept

To communicate asynchronously between two APIs deployed to a two-node on-prem cluster, the developer can use the VM Connector if the two APIs use the same domain. The VM Connector allows passing messages between different Mule applications within a single Mule runtime instance or across different instances using shared memory or persistent storage. If two APIs are deployed under the same domain, they can share resources such as VM queues and communicate asynchronously using VM Connector operations. References: https://docs.mulesoft.com/mule-runtime/4.3/vm-connector https://docs.mulesoft.com/mule-runtime/4.3/shared-resources

Mutual TLS (mTLS) is an extension of TLS that requires both parties (client and server) to present their certificates to each other during the handshake process. This way, both parties can verify each other’s identity and establish a secure connection. The authentication of the server happens before the authentication of the client, as the server sends its certificate first and then requests the client’s certificate. References:https://docs.mulesoft.com/mule-runtime/4.3/tls-configuration#mutual-authentication