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Monitoring

The state of whimsy is represented as a tree of named nodes.

Nodes, names, and strings

Each major branch is produced by a monitor. Each monitor can return a tree of nodes, or a single String, or an array of Strings. The name of the monitor is used as the name of the node produced.

Leaf nodes consist of a String, an array of Strings, or a Hash where one element in the Hash has a key of data with a value of either a String or an array of Strings.

Non-leaf nodes consist of a Hash where one element in the Hash has a key of data with a value that is a Hash of names and child nodes.

Levels

Each node is associated with a status level. Valid levels are success, info, warning, danger, and fatal. (The first four levels are modelled after Bootstrap alerts).

Default level for valid leaf nodes is success. Invalid leaf nodes (e.g., a node consisting of a nil value) have a level of danger. Only leaf nodes that in the form of a Hash can have levels. Leaf nodes that are not Hashes will be normalized into a Hash with a level and data.

Default level for non-leaf nodes is the highest level in children nodes (where fatal > danger, danger > warning, warning > info and info > success). Normally monitors will not assign level values for non-leaf nodes.

Titles

Non-leaf nodes have a title describing the contents of the children. Titles show up as tooltips in the browser.

Default for title is either a list or a count of the names of child nodes with the highest status. Again, normally monitors will not assign title values for nodes.

Text

Somewhat rare, but a node may have text which is used in place of the name of the node for display purposes (the name continues to be used to produce the anchor id for the element for linking purposes).

Internally, exceptions returned by a monitor are converted to a leaf node with a name of exception, a title containing the exception, and data consisting of a stack traceback.

Href

Leaf nodes may have a href which will be used as the target for the link used to display the contents of the leaf node (either a single String or an array of Strings).

Mtime

Anchors and the top of each major branch emanating from the root have an mtime value which indicates when that data was last updated. This is described below in the control flow section below.

Leaf nodes can have a mtime value in place of data. Such values will be converted to local time and displayed as the last update value. Hovering over such items will show the GMT value of the time specified in ISO-8601 format.

Control Flow

Fetching the https://whimsy-test.apache.org/status/ web page, which can be done either by browsers or pings, results in a call to index.cgi. If it has been more than 60 seconds since the last status update, index.cgi will call monitor.rb. Monitor.rb will load and then call each of the monitors defined in the monitors subdirectory.

Monitors are simple class methods. Monitors can assume that they are called no more often than once a minute, and are passed the normalized results of the previous call.

As monitors are called in response to a ping, they are expected to produce results in sub-second time in order to avoid the ping timing out. (Monitors are run in separate threads to minimize the total elapsed time). Monitors that perform activities that take a substantial amount of time may elect to do so less frequently than once a minute, and can take advantage of the mtime values to determine when to do so.

Results are collected into a hash, and that hash is then normalized. Normalization resolves default values for items like levels and titles recursively.

The normalized status is written to disk as status.json, and used as a response to pings that occur less than a minute after the previous status.

Alerts

The Apache Software Foundation infrastructure team uses Ping My Box to monitor status. A dozen+ servers around the world check status ever 5 minutes or so, and will report failure results to the infrastructure HipChat channel, and may in the future be configured to send pager alerts.

While the full status for whimsy is represented as a tree of nodes, each assigned one of our levels, and containing either child nodes or one or more strings, all the infrastructure team is currently concerned with is a boolean status (success and info are treated as success, and warning and danger are treated as failure) and the computed title for the root node.