Service Aggregator Pattern

Another option for eliminating microservice-to-microservice coupling is an Aggregator microservice, shown in purple in Figure 4-10.

The pattern isolates an operation that makes calls to multiple back-end microservices, centralizing its logic into a specialized microservice. The purplecheckout aggregator microservice in the previous figure orchestrates the workflow for the Checkout operation. It includes calls to several back-end microservices in a sequenced order. Data from the workflow is aggregated and returned to the caller. While it still implements direct HTTP calls, the aggregator microservice reduces direct dependencies among back-end microservices.

References:

https://docs.microsoft.com/en-us/dotnet/architecture/cloud-native/service-to-service-communication#:~:text=Service%20Aggregator%20Pattern &text=The%20pattern%20isolates%20an%20operation,logic%20into%20a%20specialized%20microservice.&text=While%20it%20still%20implements%20direct,dependencies%20among%20back%2Dend%20microservices.

Service Choreography

Service choreography is a global description of the participating services, which is defined by exchange of messages, rules of interactionand agreements between two or more endpoints. Choreography employs a decentralized approach for service composition. the decision logic is distributed, with no centralized point.

Choreography, in contrast, does not rely on a central coordinator. and all participants in the choreography need to be aware of the business process, operations to execute, messages to exchange, and the timing of message exchanges.

References:

https://stackoverflow.com/questions/4127241/orchestration-vs-choreography/33316988

Troubleshooting Oracle Functions:

There are common issues related to Oracle Functions and how you can address them.

Invoking a function returns a FunctionInvokeSubnetNotAvailable message and a 502 error (due to a DHCP Options issue)

When you invoke a function that you've deployed to OracleFunctions, you might see the following error message:

{"code":"FunctionInvokeSubnetNotAvailable","message":"dhcp options ocid1.dhcpoptions........ does not exist or Oracle Functions is not authorized to use it"}

Fn: Error invoking function. status: 502 message: dhcp options ocid1.dhcpoptions........ does not exist or Oracle Functions is not authorized to use it

If you see this error:

Double-check that a policy has been created to give Oracle Functions access to network resources.

Create Policies to ControlAccess to Network and Function-Related Resources:

Service Access to Network Resources

When Oracle Functions users create a function or application, they have to specify a VCN and a subnet in which to create them. To enable the Oracle Functions service tocreate the function or application in the specified VCN and subnet, you must create an identity policy to grant the Oracle Functions service access to the compartment to which the network resources belong.

To create a policy to give the Oracle Functions service access to network resources:

Log in to the Console as a tenancy administrator.

Create a new policy in the root compartment:

Open the navigation menu. Under Governance and Administration, go to Identity and click Policies.

Follow the instructions in To create a policy, and give the policy a name (for example, functions-service-network-access).

Specify a policy statement to give the Oracle Functions service access to the network resources in the compartment:

Allow service FaaS to use virtual-network-family in compartment

For example:

Allow service FaaS to use virtual-network-family in compartment acme-network

Click Create.

Double-check that the set of DHCP Options in the VCN specified for the application still exists.

References:

https://docs.cloud.oracle.c om/en-us/iaas/Content/Functions/Tasks/functionstroubleshooting.htm

https://docs.cloud.oracle.com/en-us/iaas/Content/Functions/Tasks/functionscre atingpolicies.htm

You can invoke a function that you've deployed to Oracle Functions in different ways:

Using the Fn Project CLI.

Using the Oracle Cloud Infrastructure CLI.

Using the Oracle Cloud Infrastructure SDKs.

Making a signed HTTP request to the function's invoke endpoint. Every function has an invoke endpoint.

Each of the above invokes the function via requests to the API. Any request to the API must be authenticated by including a signature and the OCID of the compartmentto which the function belongs in the request header. Such a request is referred to as a 'signed' request. The signature includes Oracle Cloud Infrastructure credentials in an encrypted form.

A cascading failure is a failure that grows over time as a result of positive feedback. It can occur when a portion of an overall system fails, increasing theprobability that other portions of the system fail.

the circuit breaker pattern prevents the service from performing an operation that is likely to fail. For example, a client service can use a circuit breaker to prevent further remote calls over the network when a downstream service is not functioning properly. This can also prevent the network from becoming congested by a sudden spike in failed retries by one service to another, and it can also prevent cascading failures. Self-healing circuit breakers check the downstream service at regular intervals and reset the circuit breaker when the downstream service starts functioning properly.

https://blogs.oracle.com/developers/getting-started-with-microservices-part-three