Bulk REST Callouts with Queueable Apex in Salesforce

Question:

We have a REST API callout implemented in Queueable Apex that fetches and updates HR information for related Contact records from an external system whenever a Contact is inserted or updated in Salesforce. The issue arises when a bulk insert or update operation occurs on Contact records, as this triggers multiple API calls and quickly hits governor limits. The external system does not provide a bulk API. How can we bulkify or redesign this integration so that it works efficiently without hitting limits?

Answer:

This problem occurs because each record update leads to an individual Queueable callout, which causes governor limit violations in bulk scenarios. Since the external system does not expose a bulk API, the optimization must happen on the Salesforce side by controlling how requests are batched and queued.

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One common approach is to collect all the Contact records being updated in a single Queueable or Batch process, and then process them in controlled chunks. This means grouping multiple record IDs into one Queueable execution, making a single API call per chunk instead of one per record. You can then loop through the response and update all corresponding records in Salesforce.

Here is a simplified example:

public class ContactHRIntegrationQueueable implements Queueable, Database.AllowsCallouts {
    private List<Id> contactIds;
    
    public ContactHRIntegrationQueueable(List<Id> contactIds) {
        this.contactIds = contactIds;
    }
    
    public void execute(QueueableContext context) {
        List<Contact> contacts = [SELECT Id, Email FROM Contact WHERE Id IN :contactIds];
        
        // Example: Split into smaller chunks to avoid limits
        Integer chunkSize = 10;  
        for (Integer i = 0; i < contacts.size(); i += chunkSize) {
            List<Contact> chunk = contacts.subList(i, Math.min(i + chunkSize, contacts.size()));
            
            // Make a single REST callout for this chunk
            HttpRequest req = new HttpRequest();
            req.setEndpoint('callout:HRSystem');
            req.setMethod('POST');
            req.setBody(JSON.serialize(chunk));
            
            Http http = new Http();
            HttpResponse res = http.send(req);
            
            if (res.getStatusCode() == 200) {
                // Parse and update records
                Map<String, Object> hrData = (Map<String, Object>) JSON.deserializeUntyped(res.getBody());
                // Update logic goes here
            }
        }
    }
}

public class ContactHRIntegrationQueueable implements Queueable, Database.AllowsCallouts {
    private List<Id> contactIds;
    
    public ContactHRIntegrationQueueable(List<Id> contactIds) {
        this.contactIds = contactIds;
    }
    
    public void execute(QueueableContext context) {
        List<Contact> contacts = [SELECT Id, Email FROM Contact WHERE Id IN :contactIds];
        
        // Example: Split into smaller chunks to avoid limits
        Integer chunkSize = 10;  
        for (Integer i = 0; i < contacts.size(); i += chunkSize) {
            List<Contact> chunk = contacts.subList(i, Math.min(i + chunkSize, contacts.size()));
            
            // Make a single REST callout for this chunk
            HttpRequest req = new HttpRequest();
            req.setEndpoint('callout:HRSystem');
            req.setMethod('POST');
            req.setBody(JSON.serialize(chunk));
            
            Http http = new Http();
            HttpResponse res = http.send(req);
            
            if (res.getStatusCode() == 200) {
                // Parse and update records
                Map<String, Object> hrData = (Map<String, Object>) JSON.deserializeUntyped(res.getBody());
                // Update logic goes here
            }
        }
    }
}

Explanation: This Queueable Apex class is designed to handle REST API callouts for multiple Contact records in bulk. It takes a list of Contact IDs, queries their details, and processes them in smaller chunks to avoid hitting governor limits. For each chunk, it makes a single POST callout to the external HR system, serializes the data into JSON, and then processes the response to update Salesforce records accordingly. This approach reduces the number of callouts and ensures the integration can scale for bulk operations.

Another approach is to use Platform Events or Change Data Capture (CDC). Instead of triggering immediate callouts for each DML, publish a platform event with the Contact IDs. A subscriber process (such as a Queueable or Batch Apex) can then aggregate these events over a short time window, combine them, and make fewer API calls.

If the external system has strict per-call limits but no bulk API, you can also consider building a middleware layer (like MuleSoft, AWS Lambda, or Heroku). Salesforce sends batched Contact IDs to the middleware, which then fans out and makes multiple calls to the external API. Middleware often provides more flexibility and avoids Salesforce’s synchronous limits.

Summing Up

This solution demonstrates how to manage bulk REST API callouts in Salesforce using Queueable Apex. By splitting Contact records into smaller chunks and processing them in batches, it prevents governor limit issues. The approach ensures scalable, efficient integration with external systems even when bulk operations occur.

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