Skip to main content

Scaling Policies

This post is part of a bigger topic Autoscaling Publishers in AWS.

In a previous post we talked about the Auto Scaling Groups, but we didn't go into details on the Scaling Policies. This is the purpose of this blog post.

As defined earlier, the Scaling Policies define the rules according to which the group size is increased or decreased. These rules are based on instance metrics (e.g. CPU), CloudWatch custom metrics, or even CloudWatch alarms and their states and values.


We defined a Scaling Policy with Steps, called 'increase_group_size', which is triggered first by the CloudWatch Alarm 'Publish_Alarm' defined earlier. Also depending on the size of the monitored CloudWatch custom metric 'Waiting for Publish', the Scaling Policy with Steps can add a difference number of instances to the group.

The scaling policy sets the number of instances in group to 1 if there are between 1000 and 2000 items Waiting for Publish in the queue. It also sets the group size to 2 if there are more than 2000 items in the queue.

This logic expects the Alarm is in state ALARM first, and then depending on the items in Waiting for Publish, it will set the group size accordingly.

For the other Scaling Policy, called 'decrease_group_size', the logic is a bit different. This is a simple scaling policy, which sets the group size to 0 (removes all publishers) if the Publish_Alarm is in state OK.

To notice in the image above the logic is incorrect, and I suspect this has to do with the fact AWS GUI cannot display this setup. Instead, we need to go to the CloudWatch Alarm setup GUI and setup the logic there, as per screenshot below:



Note the Actions for this alarm: 2 AutoScaling Actions, one for increase and one for decrease of group size.

For the decrease action: whenever the alarm is in state OK, perform action 'decrease_group_size', which means terminate all instances in the group.

For the increase action, whenever the alarm is in state ALARM, perform actions according to scaling policy with steps 'increase_group_size'.


Comments

Popular posts from this blog

Toolkit - Dynamic Content Queries

This post if part of a series about the  File System Toolkit  - a custom content delivery API for SDL Tridion. This post presents the Dynamic Content Query capability. The requirements for the Toolkit API are that it should be able to provide CustomMeta queries, pagination, and sorting -- all on the file system, without the use third party tools (database, search engines, indexers, etc). Therefore I had to implement a simple database engine and indexer -- which is described in more detail in post Writing My Own Database Engine . The querying logic does not make use of cache. This means the query logic is executed every time. When models are requested, the models are however retrieved using the ModelFactory and those are cached. Query Class This is the main class for dynamic content queries. It is the entry point into the execution logic of a query. The class takes as parameter a Criterion (presented below) which triggers the execution of query in all sub-criteria of a Criterio

A DD4T.net Implementation - Custom Binary Publisher

The default way to publish binaries in DD4T is implemented in class DD4T.Templates.Base.Utils.BinaryPublisher and uses method RenderedItem.AddBinary(Component) . This produces binaries that have their TCM URI as suffix in their filename. In my recent project, we had a requirement that binary file names should be clean (without the TCM URI suffix). Therefore, it was time to modify the way DD4T was publishing binaries. The method in charge with publishing binaries is called PublishItem and is defined in class BinaryPublisher . I therefore extended the BinaryPublisher and overrode method PublishItem. public class CustomBinaryPublisher : BinaryPublisher { private Template currentTemplate; private TcmUri structureGroupUri; In its simplest form, method PublishItem just takes the item and passes it to the AddBinary. In order to accomplish the requirement, we must specify a filename while publishing. This is the file name part of the binary path of Component.BinaryConten