Google gives developershigh-availability storage option and HRD Migration tool in latest update
Google has released an update to its App Engine cloud service which includes a more robust storage option that was originally developed to deal with serious performance problems the service experienced last year.
App Engine 1.6.1, released this week, includes the first full release of the High Replication Datastore (HRD) Migration Tool, which allows developers to migrate an application’s data to an application built on HRD.
This step is necessary since an application can’t be shifted from one storage option to the other as developers must choose between the two options at the time that the application is created, and the configuration can’t be changed. To begin using HRD, a developer must build a new application and then migrate the datastore.
The tool limits the downtime required to complete the migration, and allows developers to choose the precise timing of the migration, Google said.
The High Replication Datastore was originally released in January following persistent performance problems that had gone on for several months. Until now, however, the migration tool has been in experimental mode, limiting developers’ ability to take advantage of the new datastore.
“Our experience with these issues has made us rethink some of our design assumptions,” Google said at the time. “As we promised you in some of our outage reports earlier this year, we wanted to give you a more fundamental solution to the problem.”
HRD gives developers a higher level of availability by increasing the number of data centres that maintain replicas of the data, using the Paxos algorithm to perform real-time synchronisation, Google said. This allows applications to continue functioning during planned maintenance periods, as well as during outages.
Interactions do, however, include higher latency, and HRD is also significantly more expensive for developers than the standard Master/Slave storage option, the company said.
“Due to the higher cost, we thus recommend the High Replication Datastore primarily for those developers building critical applications on App Engine who want the highest possible level of availability for their application,” Google stated.
The App Engine release also introduces two new virtual server options, called front-end instance classes, offering more memory and CPU power for serving requests more quickly.
“Before today, all apps were allocated a fixed instance size no matter what the app was computing in its requests. Now, apps that need more computing power can upgrade the size of their instances,” Google stated.
The release includes two new experimental application programming interfaces (APIs), a Conversion API for converting document formats within an application and a Logs Reader API for accessing and analysing application logs.