EWD 3 Training Course Part 35: QEWD Session Locking

Oct 27, 20161 like535 views

This is part 35 of the EWD 3 Training Course. This presentation explains how QEWD supports Session locking, which prevents two simultaneously invoked requests from the same QEWD session from using the QEWD session simultaneously

Copyright © 2016 M/Gateway Developments Ltd
EWD 3 Training Course
Part 35
QEWD Session Locking
Rob Tweed
Director, M/Gateway Developments Ltd
Twitter: @rtweed

Copyright © 2016 M/Gateway Developments Ltd
QEWD Sessions
• QEWD uses the ewd-session module to provide
its Session functionality
• QEWD Session data is physically stored in your
embedded Global Storage database:
– Redis, Cache or GT.M
– Uses the DocumentStore / DocumentNode
abstraction
• All Worker processes have access to the
Session document in your Global storage
– So it doesn't matter which physical worker process
handles each requst for the same Session

Copyright © 2016 M/Gateway Developments Ltd
QEWD Sessions
• There's nothing to stop a browser / client
from sending 2 simultaneous requests to
QEWD
– If this happens, the one that arrives first at the
QEWD back-end will be dispatched to the first
available worker process
– The second request will probably be next in
the queue, and if there's another available
worker process, the second request will be
dispatched to it

Copyright © 2016 M/Gateway Developments Ltd
QEWD Sessions
• So it's possible to have two Worker
processes handling requests from the
same client and for the same QEWD
Session
• If the handler functions for these requests
modify the QEWD Session contents,
there's a risk of data corruption if they both
access / change the same Session data at
the same time

Copyright © 2016 M/Gateway Developments Ltd
QEWD Session Locking
• To prevent this happening, you can
optionally enable Session Locking.
• In this mode, the first Worker locks the
Session document for the QEWD Session
it's handling
• The second Worker tries to do the same,
but can't set the lock, so it waits
– Remember QEWD uses synchronous APIs,
so the second worker process blocks

Copyright © 2016 M/Gateway Developments Ltd
QEWD Session Locking
• When the first Worker finishes processing (by
invoking the finished() function), it releases the
Session lock
• The second Worker can now set the lock and
commence processing
– It releases the lock again when it finishes
• Note that other workers processing requests for
other Sessions won't be affected
– They will be locking/unlocking different Sessions

Copyright © 2016 M/Gateway Developments Ltd
QEWD Session Locking
• Session locking therefore forces processing of
simultaneously sent requests from the same
browser / client to be serialised
– ie requests for a specific QEWD Session will only be
handled one at a time
• Note that QEWD will process them in the order it
received them
– If you need them to be processed in a specific order, you'll need
to control the sequence within the browser / client yourself

Copyright © 2016 M/Gateway Developments Ltd
Enabling Session Locking
• Simple change to your QEWD startup file
• Add the lockSession property to the config
object
• Set its value to true

Copyright © 2016 M/Gateway Developments Ltd
Edit your QEWD Startup File
var config = {
managementPassword: 'keepThisSecret!',
serverName: 'My QEWD Server',
port: 8080,
poolSize: 2,
database: {
type: 'cache',
params: {
path: 'c:InterSystemsCache2015-2mgr’
},
lockSession: true
}
};
var qewd = require('qewd').master;
qewd.start(config);

Copyright © 2016 M/Gateway Developments Ltd
Restart QEWD
• Session locking is now enabled

This document discusses advanced microservice functionality in QEWD, including templated routes, dynamic path-defined destinations, federated composite microservices, redirection of responses, and chained microservices. It provides an example of extending a previous login microservice example to demonstrate these features. Templated routes allow variable path components that are passed to handler functions. Security is improved by adding authentication against JSON web tokens in the beforeMicroserviceHandler function.

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