assigntransactionid.md

Assign ‘TransactionId’ to each log statement

One Paragraph Explainer

A typical log is a warehouse of entries from all components and requests. Upon detection of some suspicious line or error it becomes hairy to match other lines that belong to the same specific flow (e.g. the user “John” tried to buy something). This becomes even more critical and challenging in microservices environment when a request/transaction might span across multiple computers. Address this by assigning a unique transaction Id value to all the entries from the same request so when detecting one line one can copy the id and search for every line that has similar transaction Id. However, achieving this In Node is not straightforward as a single thread is used to serve all requests –consider using a library that that can group data on the request level – see code example on the next slide. When calling other microservice, pass the transaction Id using an HTTP header “x-transaction-id” to keep the same context.

Code example: typical nginx configuration

//when receiving a new request, start a new isolated context and set a transaction Id. The following example is using the NPM library continuation-local-storage to isolate requests
 
var createNamespace = require('continuation-local-storage').createNamespace;
var session = createNamespace('my session');
    router.get('/:id', (req, res, next) => {
    session.set('transactionId', 'some unique GUID');
    someService.getById(req.params.id);
    logger.info('Starting now to get something by Id');
}//Now any other service or components can have access to the contextual, per-request, data
class someService {
    getById(id) {
        logger.info(“Starting now to get something by Id”);
        //other logic comes here
    }
}//Logger can now append transaction-id to each entry, so that entries from the same request will have the same value
class logger{
    info (message)
    {console.log(`message ${session.get('transactionId')}`);}
}

What Other Bloggers Say

From the blog ARG! TEAM:

...Although express.js has built in static file handling through some connect middleware, you should never use it. Nginx can do a much better job of handling static files and can prevent requests for non-dynamic content from clogging our node processes...