Conformity Monkey — Keeping your cloud instances following best practices

by Michael Fu and Cory Bennett, Engineering Tools

Cloud computing makes it much easier to launch new applications or start new instances. At Netflix, engineers can easily launch a new application in Asgard with a few clicks. With this freedom there are sometimes consequences where launched applications or instances may not follow some best practices. This can happen when an engineer isn’t familiar with best practices or when those practices have not been well publicized. For example, some required security groups may be missing from instances and can cause security gaps. Or perhaps a health check url is not defined for instances in Eureka which would result in automatic failure detection and failover being disabled.

What is Conformity Monkey?

At Netflix, we use Conformity Monkey, another member of Simian Army, to check all instances in our cloud for their conformity. Today, we are proud to announce that the source code for Conformity Monkey, is now open and available to the public. Conformity Monkey is a service which runs in the Amazon Web Services (AWS) cloud looking for instances that are not conforming to predefined rules for the best practices. Similar to Chaos Monkey and Janitor Monkey, the design of Conformity Monkey is flexible enough to allow extending it to work with other cloud providers and conformity rules. By default, conformity check is performed every hour. The schedule can be easily re-configured to fit your business’ need.

Conformity Monkey determines whether an instance is nonconforming by applying a set of rules on it. If any of the rules determines that the instance is not conforming, the monkey sends an email notification to the owner of the instance. We provide a collection of conformity rules in the open sourced version that are currently used at Netflix and believed general enough to be used by most users. The design of Conformity Monkey also makes it simple to customize rules or to add new ones.

There can be exceptions when you want to ignore warnings of a specific conformity rule for some applications. For example, a security group to open a specific port probably is not needed by instances of some applications. We allow you to customize the set of conformity rules to be applied to a cluster of instances by excluding unneeded ones.

How Conformity Monkey Works

Conformity Monkey works in two stages: mark and notify. First, Conformity Monkey loops through all autoscaling groups in your cloud and applies the specified set of conformity rules to the instances in each group. If any conformity rule determines an instance as not conforming, the autoscaling group is marked as nonconforming and the instances that break the rule are recorded. Every autoscaling group is associated with an owner email, which can be obtained from an internal system, or can be set in a configuration file. The simplest way is using a default email address, e.g. your team’s email list for all the autoscaling groups. Conformity Monkey sends email notification about the nonconforming groups to the owner, with the details of the broken conformity rule and the instances that failed the conformity check. The application owners can then take necessary actions to fix the failed instances or to exclude the conformity rule if they believe the conformity check is not necessary for the application. We allow you to set different frequency for conformity check and notification. For example, at Netflix, conformity check is performed every hour, and notification is only sent once per day at noon time. This reduces the number of emails people receive about the same conformity warning. The real-time result of conformity check for every autoscaling group is shown in a separate UI.

Configuration and Customization

The conformity rules for each autoscaling group, and the parameters used to configure each individual rule, are all configurable. You can easily customize Conformity Monkey with the most appropriate set of rules for your autoscaling groups by setting Conformity Monkey properties in a configuration file. You can also create your own rules, and we encourage you to contribute your conformity rules to the project so that all can benefit.

Storage and Costs

Conformity Monkey stores its data in an Amazon SimpleDB table by default. You can easily check the SimpleDB records to find out the last conformity check results for your autoscaling groups. At Netflix we have a UI for showing the conformity check results and we have plans to open source it in the future as well.

There could be associated costs with Amazon SimpleDB, but in most cases the activity of Conformity Monkey should be small enough to fall within Amazon’s Free Usage Tier. Ultimately the costs associated with running Conformity Monkey are your responsibility. For your reference, the costs of Amazon SimpleDB can be found at


Conformity Monkey helps keep our cloud instances following best practices. We hope you find Conformity Monkey to be useful for your business as well. We’d appreciate any feedback on it. We’re always looking for new members to join the team. If you are interested in working on great open source software, take a look at for current openings!

Conformity Monkey Links

Netflix Cloud Platform

Amazon Web Services

See Also:

Originally published at on May 29, 2013.

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Learn about Netflix’s world class engineering efforts, company culture, product developments and more.

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