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Senlin Feature Request Pipeline
This document records the feature requests the developer team has received and considered. This document SHOULD NOT be treated as a replacement of the blueprints (or specs) which already accompanied with a design. The feature requests here are meant to be a pipeline for mid-term goals that Senlin should strive to achieve. Whenever a feature can be implemented with a practical design, the feature should be moved to a blueprint (and/or specs) review.
This document SHOULD NOT be treated as a replacement of the TODO file the development team is maintaining. The TODO file records actionable work items that can be picked up by any developer who is willing to do it, while this document records more general requirements that needs at least a draft design before being worked on.
High Priority
Event Listener
To make Senlin responsive to events published by other OpenStack services, an event subscriber is needed so that Senlin can receive notifications from sources such as Ceilometer, Nova, or Zaqar.
This is of a high priority because Senlin needs it as one of its HA solutions.
Scavenger Process
Senlin needs a scavenger process that runs as a background daemon. It is tasked with cleansing database for old data, e.g. event records. Its behavior must be customizable because users may want the old records to be removed or to be archived in a certain way.
Fault Tolerance
Senlin in most cases will be managing clusters with nodes distributed somewhere. One problems inherent to such a distributed architecture is about partial failures, communication latencies, concurrency, consistency etc. There are hardware/software failures expected. Senlin must remain operational in the face of such failures.
Middle Priority
Horizon Plugin
Senlin needs a plug-in at the OpenStack dashboard side so that users can interact with the service in a more user-friendly way.
User Defined Actions
Actions in Senlin are mostly built-in ones at present. There are requirements to incorporate Shell scripts and/or other structured software configuration tools into the whole picture. One of the option is to provide a easy way for Senlin to work with Ansible, for example.
CoreOS based Container Support
To Senlin, CoreOS is just another VM image. However, CoreOS provides some builtin support to Container/Docker and it provides clustering facility for user applications.
Define and Enforce Quotas
There is a potential request to limit how many clusters a user can create, how large a cluster can become.
Event Notification
Event notification is a feature that enables an external tool to subscribe to events sent from Senlin when interesting things happen. One option is to use the messaging service provided by the Zaqar project.
Customizable Batch Processing
An important non-functional requirement for Senlin is the scale of clusters it can handle. We will strive to make it handle large scale ones, however that indicates that we need to improve DB accesses in case of heavy loads. One potential tradeoff is to introduce an option for users to customize the size of batches when large number of DB requests pouring in.
Use Barbican to Store Secrets
Currently, Senlin uses the cryptography package for data encryption and decryption. There should be support for users to store credentials using the Barbican service, in addition to the current solution.
Use VPNaaS to Build Cross-Region/Cross-Cloud
When buidling clusters that span more than one region or cloud, there are requirements to place all cluster nodes on the same VPN so that workloads can be distributed to the nodes as if they sit on the same network.
Make Use of Nova ServerGroup API
When creating a cluster of Nova servers, Senlin needs to work with Nova and its scheduler to provide sophisticated scheduling decisions. While a user do not necessarily have control over the admin plane, he or she does have a right to express their requirements in an abstract manner.
Low Priority
Vertical Scaling
Though Senlin is mainly concerns about the horizontal scaling in/out support, there are possibilities/requirements to scale nodes in the vertical direction. Vertical scaling means automatically adding compute/storage/network resources to cluster nodes. Depending on the support from corresponding services, this could be explored.
Replace Green Threads with Python Threading
Senlin is now using green threads (eventlets) for async executions. The eventlets execution model is not making the use of multi-processing platforms in an efficient way. Senlin needs a scalable execution engine, so native multi-threading is needed.
Metrics Collection
Senlin needs to support metric collections about the clusters and nodes it manages. These metrics should be collectable by the ceilometer service, for example.
AWS Compatible API
There are requirements for Senlin to provide a AWS compatible API layer so that existing workloads can be deployed to Senlin and AWS without needing to change a lot of code or configurations.
Integration with Mistral
There are cases where the (automated) operations on clusters and nodes form a workflow. For example, an event triggers some actions to be executed in sequence and those actions in turn triggers other actions to be executed.
Support to Suspend/Resume Operations
A user may want to suspend/resume a cluster or an individual node. Senlin needs to provide a generic definition of 'suspend' and 'resume'. It needs to be aware of whether the profile and the driver support such operations.
Support to Scheduled Actions
This is a request to trigger some actions at a specified time. One typical use case is to scale up a cluster before weekend or promotion season as a preparation for the coming burst of workloads.
Interaction with Congress
This is of low priority because Senlin needs a notification mechanism in place before it can talk to Congress. The reason to interact with Congress is that there could be enterprise level policy enforcement that Senlin has to comply to.
Integration with Tooz
There is potential requirement to do a better coordination between nodes in a cluster. That is where the Tooz project can be leveraged.