3 min read

Yesterday, Tumblr announced the open sourcing of three tools developed at Tumblr itself, that will help developers integrate Kubernetes into their workflows. These tools were developed by Tumblr throughout their eleven-year journey to migrate their workflow to Kubernetes with ease.
These are the 3 tools and their features as listed on the Tumblr blog:

#1 k8s- sidecar injector

Containerizing complex applications can be time-consuming. Sidecars come as a savior option, that allows developers to emulate older deployments with co-located services on Virtual machines or physical hosts. The k8s-sidecar injector dynamically injects sidecars, volumes, and environment data into pods as they are launched. This reduced the overhead and work involved in copy-pasting code to add sidecars to a developer’s deployments and cronjobs. What’s more, the tool listens to the specific sidecar to be injected, contained within the Kubernetes API for Pod launch. This tool will be useful when containerizing legacy applications requiring a complex sidecar configuration.

#2 k8s-config-projector

The k8s-config projector is a command line tool that was generated out of the necessity of accessing a subset of configuration data (feature flags, lists of hosts/IPs+ports, and application settings) and a need to be informed as soon as this data changes. Config data defines how deployed services operate at Tumblr.

Kubernetes ConfigMap resource enables users to provide their service with configuration data. It also allows them to update the data in running pods without redeployment of the application. To use this feature to configure Tumblr’s services and jobs in a Kubernetes-native manner, the team had to bridge the gap between their canonical configuration store (git repo of config files) to ConfigMaps.


k8s-config-projector combines the git repo hosting configuration data with “projection manifest” files, that describe how to group/extract settings from the config repo and transmute them into ConfigMaps.

Developers can now encode a set of configuration data that the application needs to run into a projection manifest. The blog states that ‘as the configuration data changes in the git repository, CI will run the projector, projecting and deploying new ConfigMaps containing this updated data, without needing the application to be redeployed’.

#3 k8s-secret-projector

Tumblr stores secure credentials (passwords, certificates, etc) in access controlled vaults. With k8s-secret-projector tool, developers will now be able to request access to subsets of credentials for a given application. This can be done now without granting the user access to the secrets as a whole.

The tool ensures applications always have the appropriate secrets at runtime, while enabling automated systems including certificate refreshers, DB password rotations, etc to automatically manage and update these credentials, without the need to redeploy/restart the application.
It performs the same by combining two repositories- projection manifests and credential repositories. A Continuous Integration (CI) tool like Jenkins will run the tool against any changes in the projection manifests repository. This will generate new Kubernetes Secret YAML files which will lead to the Continuous Deployment to deploy the generated and validated Secret files to any number of Kubernetes clusters. The tool will allow secrets to be deployed in Kubernetes environments by encrypting generated Secrets before they touch the disk.

You can head over to Tumblr’s official blog for examples on each tool.

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