Author Archives: Aurélien Pelletier

Google Cloud Platform technical qualification training : Cloud SQL

Not much to say about Cloud SQL, it is simply a fully managed mysql database version 5.5 and 5.6.

Fast connection to App & Compute Engine but accessible from anywhere. (you have to enable the access)

Google can manage replication for you. mysql instance are brought up on demand and can go away after 4 hours of inactivity.

Up to 500 GB per database






Google Cloud Platform technical qualification training: App Engine

I’ve just spend the week at the Google office in London to attend the CP300 course. I thought a good way to prepare for the certification exams would be to put down my notes on my blog…

Thanks to Ignacio who was leading the training.

The first two days were dedicated to Google App Engine.
App Engine is all about building scalable, reliable and cost effective web application the Google way, it :

  • Leverages Google CDN to serve static ressources
  • Use Stateless application server with automatic horizontal scaling
  • Use a NoSql datastore (you can also connect it to a relationnal database, cloud SQL, if needed)

You can configure the way it scales by tweaking pending latency and the number of idle instances. This will impact the performance and the cost of your application.

Instance on Appengine can stop and start frequently, this means you should avoid framework with long start-up time such as Spring or JPA. For depency injection prefer Guice or Dagger (injection is done at compile time)

There is a status console to check if all Google services runs normally. You can also receive notification about downtime by subscribing to this group.

The App Engine console let you monitor quotas usages, very important, most errors on App Engine append because of quota limitations. Of course you can pay to remove those limits. You set a maximum daily budget to make sure you won’t suffer from a denied of service attack on your credit card !

You can deploy and run in parallel multiple versions of the same app (blue/green deployment out of the box)

The app stat tool let you analyze performances.

Authentication & Authorization

GAE provides a service to handle Authentication & Authorization for you. It will use Google account or an openId provider. You can also integrate GAE with an enterprise SSO solution but it requires a Google Apps for business account.

Authorization to access other google API (calendar, storage, compute, …) is done with OAuth2.0.
You can try service calls and Oauth2.0 in the playground

The Datastore

This is the heart of App Engine, you better understand this if you wan’t your application to run well on App Engine.

The GAE datastore is based on Google BigTable, it provides strong consistency for single row but eventual consistency for multi row level.
Every row contains an entity of a certain kind. An entity has a key and properties, properties can be multi-valued.

An entity can have a parent to form an entity group (a single entity without parent count as an entity group). Entity group are usefull to force strong consistency when writing data.

Data on bigtable is distributed by key, if you specify the key yourself make sure it is random enough to get a good distribution of content on the underlining hardware and better performance.

The DataStore is optimized for read queries. Datastore always use an index to read data. All indexes are sorted and distributed on multiple machines.
Queries on the datastore are executed as index scan on bigtable => it’s very fast (the query performance scale with the size of the result not the size of the dataset) but it comes with a few limits:
– You can’t query without an index (indexed can be automaticaly created, beware of their size)
– Queries on multi-valued properties can lead to combinatorial Explosion and big indexes
– Missing properties is not equal to Null/none
– Inequality filter (!=) are limited to one property per query (this is because it is implemented as x< AND x> to use one sorted index)
– no JOIN (use denormalization)
– no aggregation queries (Group by, sum, having, avg, max, min, …) (instead use special entities that maintains counts) see sharding counter pattern
– creating a new index on large set can be long

Indexes are not immediatly updated when writing but ancestor queries force the index update to complete to get strong consistency.

For transaction the datastore use snapshot isolation and optimistic concurrency
Transcation can’t affect more than 5 entity groups
Can’t make more than 5 updates per second to an entity group
A transaction can’t take more than 60 seconds

Memcache, TaskQueue, Cron

GAE provides Memcache as a service to improve performance and reduce application cost. A memcache query can be ten times faster than a datastore query. Memcache can be used as a read/Write cache to the datastore

GAE provides a taskQueue service to executed asynchronous work :

  • push queues are managed by App Engine
  • pull queues are manually managed

Tasks can by enqueued in a transaction but will execute outside the transaction
A task is a GET or POST request
GAE execute as many task as possible following the token bucket algorithm
there is
– a bucket size (maximum number of tasks that can be launch at once)
– a token refresh rate (how fast the bucket replenish)
– a maximum number of concurrent requeste

If a task failed it will be re-tried according to the retry policy.
There is a 10 minutes execution limit on front-end instance (instead of 1 min for synchronous requests)

GAE also provides a cron service that you can configure in an xml or yaml file.

My schedule for Google I/O 2014

This year Google I/O will be about DDD, have you read the blue book ? Oh wait, sorry, it’s not about Domain Driven Design but Design, Develop, Distribute. Interesting to see that Google choose to replace the more common “Run” theme with a Distribute one. It feels like they are saying don’t worry anymore about how you will run your application, just use our cloud. But instead think how you will Distribute your mobile application… on google store of course.

We can expect a lot of announcements and sessions around Android. And a lot more, as you can see in the list of sessions I’m planning to attend. Can’t wait to learn more about Docker, Polymer, DevOps and the Google cloud platform !

Day one June 25

Day 2 June 26

Et en attendant…

Je me promène
San Francisco House San Francisco Parking


10 ans

Il y a 10 ans, le 3 avril 2004 j’ouvrais ce blog. Google n’était encore qu’un moteur de recherche performant… Amazon qu’un libraire, Face… FaceQuoi ?? Les téléphones n’étaient pas smart et Nokia dominait le marché.

Il y a 10 ans Google lançait Gmail, un 1ere Avril, 1 Go de stockage gratuit, une application web aussi réactive qu’un client lourd, la bonne blague… Eh oui Ajax n’était encore qu’une marque de détergent. Subversion était un outil acceptable pour gérer les sources, Flex une solution d’avenir, Struts était en version 1 tout comme Spring, javascript était tout juste bon à ouvrir des pop-ups. Chrome n’existait pas, IE6 s’était imposé face à Netscape.

Il y a 10 ans la France votait la Loi pour la confiance dans l’économie numérique et aujourd’hui il faut écrire un rapport pour mettre en valeur les développeurs alors qu’il y a longtemps que le reste du monde a compris que le logiciel dévore le monde

Depuis 10 ans ce ne sont pas les sujets qui manquent, je vais profiter de cet anniversaire pour ranimer ce blog, rendez-vous dans 10 ans.

Des tweets et des plus n°22 – Et ça sert à quoi ?

La vérité sur le chiffrage en Sociétés de Services en Logiciels Libres : “Nous aimons coder. Coder ne nous coûte pas car c’est notre plaisir. D’ailleurs, nous codons  gratuitement une bonne partie de notre temps (dans le cadre de nos contributions open sources). Le reste de notre travail, en revanche, nous coûte.”

Stop Using Story Points :  “Like researchers of fast food, we now know that the Agile Happy Meal contains unnatural ingredients that decrease agility and cause process indigestion.”

What’s my IT strategy? : “Take a company’s IT strategy […] Now remove XXX […] What is left, is the IT strategy”

Java feature applicatbility : “I group Java features in three categories: day to day, occasionally and never (frameworks and libraries only). The rule is simple: if you find yourself using given feature more often then suggested, you are probably over-engineering”