1. Why doesn’t Savanna use Heat to provision VMs?
Generally using Heat underneath for infrastructure provisioning looks reasonable. In a tactic perspective there are few factors making Heat usage underneath Savanna problematic:
- Heat stability for Grizzly release. Savanna currently maintains Grizzly+ compatibility.
- Installation of large Hadoop clusters (100+ nodes). Will be addressed by proposed architecture changes.
- Anti-affinity support for HDFS redundancy in cloud environment
- Circular dependencies - we should generate ‘/etc/hosts’ for all instances in provisioned cluster. We can’t use cloud init for this directly. There are a couple possible solutions using Heat, but none of them looks like a straightforward solution.
- Level of complexity. We try to keep things as simple as possible. Adding extra layer will increase overall complexity of the solution. In addition both Savanna and Heat under active development changing lots of internals and even APIs and will require extra effort to coordinate.
Once Heat supports all the features we need, it will make sense to use Heat to provision VMs for Savanna. Here is what we’ll do: - Create a wiki page with text from this email - Create a list of requirements for Heat
Once Heat fulfills all these requirements we will be able and should use Heat for VM provisioning.
2. Why we need Savanna? Can’t we use Heat to do what Savanna does?
- Savanna provides bunch of Hadoop-specific features. It’ll be hard to provide them as Heat plugin
- Savanna provides Hadoop-specific APIs and functionality. Heat use cases are mostly around provisioning/deployment.
- Savanna provides integration with various Hadoop distributions through pluggable mechanism
Now, more details on each item. Hadoop specific features:
- Tight Swift integration. Hadoop can read and write from/to Swift object storage. Savanna provides required configs for the Hadoop cluster.
- Usage of anti-affinity to preserve data-redundancy of HDFS nodes
Hadoop-specific APIs and functionality:
- Hadoop cluster scaling
- Elastic Data Processing: https://wiki.openstack.org/wiki/Savanna/EDP
Integration with Hadoop distributions through pluggable mechanism:
Usually Hadoop cluster deployment is a multi-step operation. First step is to install management console (for instance Apache Ambari). Second step is to communicate with management console through REST API to provision Hadoop on the cluster. Savanna wraps all this operations under well-defined API.
3. Why can’t Savanna be used as a plugin for Heat?
It should be and it will be someday.