How Monzo Isolated Their Microservices Using Kubernetes Network Policies


Monzo’s safety team shared their story about applying Kubernetes community policies utilizing Calico APIs to offer isolation amid 1500 microservices.

Monzo is a cell-only electronic financial institution that runs its core infrastructure on AWS. Using Kubernetes for hosting its microservices, Monzo takes advantage of Apache Cassandra as its most important databases, Apache Kafka for messaging and Go for most of its application code. The stability team at Monzo engineering adopted zero rely on networking as a single of their objectives. A zero have confidence in platform functions on the principle that no entities – inside of or exterior the community –  are trustworthy to entry private information until they are confirmed. Each and every services in Monzo’s backend would be permitted to discuss to only a pre-accredited listing of expert services. Monzo has all over 1500 products and services, with in excess of 9300 inter-provider interactions, building this a hard process. The workforce employed Calico specific network insurance policies on Kubernetes to supply this isolation, soon after building a tailor made toolset that derives the policies by doing code evaluation.

The staff isolated just one support to examination out their preliminary method. They wrote a tailor made resource named rpcmap which discovers inter-support dependencies from static code evaluation. According to Jack Kleeman, Backend Engineer at Monzo, they chose static assessment over observation for the duration of integration screening or all through runtime simply because:


Monzo has a lot of code paths – there is just not an integration examination for everything. And for runtime, just simply because one thing is hardly ever identified as isn’t going to suggest it is really hardly ever identified as a financial institution can have annually processes.


The rules experienced to be stored in a workable and readable way with no disrupting how the current products and services get the job done. The crew made use of Kubernetes’ NetworkPolicy to implement the discovered principles. Monzo works by using the Calico networking plugin to apply Kubernetes network procedures. This original technique was brittle in conditions of testability, and put the onus of maintaining the rule listing on the staff controlling the invoked provider. Yet another drawback cited was that the dev teams would have to edit Kubernetes config files by hand.

To remedy these, Kleeman states that “we spoke to the Calico group about screening network guidelines, and uncovered that we could use some options of Calico that aren’t available by Kubernetes to make our policies testable.” One particular of these attributes authorized website traffic that would generally be disallowed by community procedures, followed by logging this sort of conditions. Kubernetes network policies operate on selectors and labels, and in the absence of any procedures Kubernetes makes it possible for all communication concerning pods. Monzo configured their plan to run at the stop, and monitored their network traffic to determine out which services would have dropped packets.

Soon after this, the workforce switched the list of authorized site visitors for a company to be a assets of the invoking company, instead of the desired destination assistance. Companies employed labels to declare which providers they wanted obtain to in the policy’s ingress spec. To manage services that call a significant range of other kinds, e.g. monitoring, companies have been grouped by “services-type” and the very same principle used devoid of owning to record all the particular person expert services. rpcmap was configured to run on every single dedicate, and the deployment pipeline would convert the rule documents into provider labels. The workforce ideas to implement this making use of a service mesh in its place of in the CNI (Container Community Interface) layer in the future, owning by now moved to a tailor made mesh employing Envoy.

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