Satellite

Satellite monitors, alerts on, and self-heals your Mesos cluster.

Overview

Satellite currently serves three functions, each adding functionality to Mesos:

1. Most importantly, Satellite Master directly monitors Mesos masters and receives monitoring information from Mesos slaves through Satellite Slaves, producing a Riemann event stream for aggregate statistics of the cluster (e.g., utilization, number of tasks lost) as well as events specific to the masters (e.g., how many leaders are there).

   As Satellite embeds Riemann, you can do anything you would usually do with a Riemann event stream. You can configure to alert (e.g., email and pagerduty), feed your dashboards, and trigger whitelist updates. If you already have a primary Riemann server, you can forward events to that and contain all or some of the stream eventing logic there; the power is yours. You can look at our recipes in src/recipes.clj for patterns we have found useful.

2. Satellite provides a REST interface for interacting with the Mesos master whitelist. The whitelist is a text file of hosts to which the master will consider sending tasks. Satellite ensures that update requests are consistent across the Mesos masters. See Whitelist below for a more detailed explanation of the model for interacting with the whitelist.

3. Satellite can provide a REST interface for accessing cached Mesos task metadata. To be very clear, Satellite does not cache the metadata, simply an interface to retrieve it, if it has been cached. This is useful if you have persisted task metadata to get around the weak persistence guarantees currently offered by Mesos. This feature is optional.

Whitelist

As we said above, the Mesos whitelist is a text file of hosts to which the master will consider sending tasks. Satellite adds two additional conceptual whitelists to the mix:

1. A managed whitelist: Hosts that have been entered automatically in response to your Riemann configuration.
2. A manual whitelist: If a host is in this whitelist, its status overrides that in the managed whitelist. This is to allow manual override. The interface to this whitelist is in the PUT and DELETE REST endpoints.

A periodic merge operation merges these two to the whitelist file that Mesos observes.

Architecture

High level

There are two kinds of Satellite processes: satellite-masters and satellite-slaves. For each mesos-master and mesos-slave process, there is a satellite-master and satellite-slave process watching it respectively.

| Follower         | Leader           | Follower         |
|------------------|------------------|------------------|
| mesos-master     | mesos-master     | mesos-master     |
| satellite-master | satellite-master | satellite-master |

      ^               <-  ^  ->                 ^
      |  -> ->          \ | /           <-  <-  |
      | / _/             \|/              \,_ \ |

| satellite-slave | satellite-slave | satellite-slave |
| mesos-slave     | mesos-slave     | mesos-slave     |

Little lower

satellite-master embeds Riemann and satellite-slave embeds a Riemann client. satellite-slaves send one type of message to all the satellite-masters, a Riemann event that is the result of a user-specified test.

You can use Riemann's powerful stream processing DSL to act on the events your slave is sending the masters--email, alert, turn hosts on or off--it's up to you!

We've provided some very, very basic recipes and are interested in adding more, so please send a pull request if you think anything would serve the larger community.

Deploying Satellite

If you're deploying Satellite to a Mesos cluster, you might find that installing and configuring it on all of your hosts involves some repetitive busy work. To help you automate these tasks, we've provided some Ansible Roles.

Contributing

We need all contributors to fill out our Contributor License Agreement found in /cla before we can accept any code or pull requests.

&c

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