Final Answer:
When making a callout from a trigger, the callout must be done asynchronously using asynchronous Apex methods, such as future methods or Queueable Apex, to ensure that the trigger process doesn't block while waiting for the external service's response.
Step-by-step explanation:
When a trigger initiates a callout to an external service, it's crucial to execute the callout asynchronously to prevent blocking the trigger process. Trigger processes, which are part of the Salesforce platform, have transactional boundaries, and making synchronous callouts directly within a trigger could lead to performance issues and timeouts.
To address this, Salesforce provides asynchronous Apex methods, such as future methods and Queueable Apex. These methods allow the trigger to delegate the callout operation to a separate execution context, freeing up the trigger process to continue without waiting for the external service's response. Future methods are suitable for simple scenarios, while Queueable Apex provides more flexibility and control over the execution order.
By leveraging asynchronous Apex, developers can design trigger processes that seamlessly integrate with external services while maintaining the efficiency and responsiveness of the Salesforce platform. This approach aligns with best practices for building scalable and performant solutions on the Salesforce platform, ensuring that trigger execution is not adversely affected by external service latency or unavailability.