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VAST v1.1

· 6 min read
Dominik Lohmann

Dear community, we are excited to announce VAST v1.1, which ships with exciting new features: query language plugins to exchange the query expression frontend, and compaction as a mechanism for expressing fine-grained data retention policies and gradually aging out data instead of simply deleting it.

Query Language Plugins

VAST features a new query language plugin type that makes it possible to exchange the querying frontend, that is, replace the language in which the user writes queries. This makes it easier to integrate VAST into specific domains without compromising the policy-neutral system core.

The first instance of the query language plugin is the sigma plugin, which make it possible to pass Sigma rules as input instead of a standard VAST query expression. Prior to this plugin, VAST attempted to parse a query as Sigma rule first, and if that failed, tried to parse it as a VAST expression. The behavior changed in that VAST now always tries to interpret user input as VAST expression, and if that fails, goes through all other loaded query language plugins.

Moving forward, we will make it easier for integrators to BYO query language and leverage VAST as an execution engine. We have already experimented with Substrait, a cross-language protobuf spec for query plans. The vision is that users can easily connect any query language that compiles into Substrait, and VAST takes the query plan as binary substrait blob. Substrait is still a very young project, but if the Arrow integration starts to mature, it has the potential to enable very powerful types of queries without much heavy lifting on our end. We already use the Arrow Compute API to implement generic grouping and aggregation during compaction, which allows us to avoid hand-roll and optimize compute kernels for standard functions.

Compaction Plugin

Compaction is a feature to perform fine-grained transformation of historical data to manage a fixed storage budget. This gives operators full control over shrinking data gradually—both from a temporal and spatial angle:

Spatial: Traditionally, reaching a storage budget triggers deletion of the oldest (or least-recently-used) data. This is a binary decision to throw away a subset of events. It does not differentiate the utility of data within an event. What if you could only throw away the irrelevant parts and keep the information that might still be useful for longitudinal investigations? What if you could aggregate multiple events into a single one that captures valuable information? Imagine, for example, halving the space utilization of events with network flow information and keeping them 6 months longer; or imagine you could roll up a set of flows into a traffic matrix that only captures who communicated with whom in a given timeframe.

By incrementally elevating data into more space-efficient representations, compaction gives you a much more powerful mechanism to achieve long retention periods while working with high-volume telemetry.

Temporal: data residency regulations often come with compliance policies with maximum retention periods, e.g., data containing personal data. For example, a policy may dictate a maximum retention of 1 week for events containing URIs and 3 months for events containing IP addresses related to network connections. However, these retention windows could be broadened when pseudonomyzing or anonymizing the relevant fields.

Compaction has a policy-based approach to specify these temporal constraints in a clear, declarative fashion.

Compaction supersedes both the disk monitor and aging, being able to cover the entire functionality of their behaviors in a more configurable way. The disk monitor remains unchanged and the experimental aging feature is deprecated (see below).

Updates to Transform Steps

Aggregate Step

Transforms → Pipelines

In VAST v2.2, we renamed transforms to pipelines, and transform steps to pipeline operators. This caused several configuration key changes. Additionally, we renamed the aggregate operator to summarize. Please keep this in mind when reading the example below and consult the documentation for the up-to-date syntax.

The new aggregate transform step plugin allows for reducing data with an aggregation operation over a group of columns.

Aggregation is a two-step process of first bucketing data in groups of values, and then executing an aggregation function that computes a single value over the bucket. The functionality is in line with what standard execution engines offer via "group-by" and "aggregate".

Based on how the transformation is invoked in VAST, the boundary for determining what goes into a grouping can be a table slice (e.g., during import/export) or an entire partition (during compaction).

How this works is best shown on example data. Consider the following events representing flow data that contain a source IP address, a start and end timestamp, the number of bytes per flow, a boolean flag whether there is an associated alert, and a unique identifier.

{"source_ip": "", "num_bytes": 87122, "start": "2022-02-22T10:36:40", "end": "2022-02-22T10:36:47", "alerted": false, "unique_id": 1}
{"source_ip": "", "num_bytes": 62335, "start": "2022-02-22T10:36:43", "end": "2022-02-22T10:36:48", "alerted": false, "unique_id": 2}
{"source_ip": "", "num_bytes": 640, "start": "2022-02-22T10:36:46", "end": "2022-02-22T10:36:47", "alerted": true, "unique_id": 3}
{"source_ip": "", "num_bytes": 2162, "start": "2022-02-22T10:36:49", "end": "2022-02-22T10:36:51", "alerted": false, "unique_id": 4}

We can now configure a transformation that groups the events by their source IP address, takes the sum of the number of bytes, the minimum of the start timestamp, the maximum of the end timestamp, and the disjunction of the alerted flag. Since the unique identifier cannot be aggregated in a meaningful manner, it is discarded.

- aggregate:
- source_ip
- num_bytes
- start
- end
- alerted

After applying the transform, the resulting events will look like this:

{"source_ip": "", "num_bytes": 89924, "start": "2022-02-22T10:36:40", "end": "2022-02-02T10:36:51", "alerted": true}
{"source_ip": "", "num_bytes": 62335, "start": "2020-11-06T10:36:43", "end": "2020-02-22T10:36:48", "alerted": false}

Unlike the built-in transform steps, aggregate is a separate open-source plugin that needs to be manually enabled in your vast.yaml configuration to be usable:

- aggregate

Rename Step

The new rename transform step is a built-in that allows for changing the name of the schema of data. This is particularly useful when a transformation changes the shape of the data. E.g., an aggregated suricata.flow should likely be renamed because it is of a different layout.

This is how you configure the transform step:

- from: suricata.flow
to: suricata.aggregated_flow

Project and Select Steps

The built-in project and select transform steps now drop table slices where no columns and rows match the configuration respectively instead of leaving the data untouched.


The msgpack encoding no longer exists. As we integrate deeper with Apache Arrow, the arrow encoding is now the only option. Configuration options for msgpack will be removed in an upcoming major release. On startup, VAST now warns if any of the deprecated options are in use.

VAST’s aging feature never made it out of the experimental stage: it only erased data without updating the index correctly, leading to unnecessary lookups due to overly large candidate sets and miscounts in the statistics. Because time-based compaction is a superset of the aging functionality (that also updates the index correctly), we will remove aging in a future release. VAST now warns on startup if it’s configured to run aging.