Filter, reshape, and redact logs before export with Transformers

Logpush delivers logs in batches as quickly as possible, enabling Cloudflare to provide information almost in real time. During our recent Birthday Week, we made Logpush available on all self-serve plans and Transformers generally available.

Those changes were among eight major updates to Cloudflare Observability and reflect our commitment to make every Cloudflare feature available to everyone. This post takes a deeper look at how Transformers work inside Logpush's export pipeline. Observability teams use Logpush to export Cloudflare logs to security information and event management systems (SIEMs), analytics platforms, and object storage. Before those logs reach their destination, teams may need to remove health checks, omit sensitive fields, or reshape records for dashboards and investigations. Today, this often requires a separate processing service that teams must deploy, scale, monitor, and maintain.

For example, a team that collects logs from multiple CDNs can add a static provider field to normalize records before they reach its analytics platform. Teams also pay to export, ingest, and store records they discard as soon as they arrive, so filtering them before delivery can reduce downstream data volume and cost.

With Transformers, that processing moves into the Logpush export workflow.Teams define a SQL query to filter records, redact sensitive data, and reshape the output by adding, renaming, removing, or nesting fields. Logpush applies the query before export, so each destination receives data in the form it needs. We made this workflow simple for customers by embedding a SQL transformation engine in Logpush's high-throughput export pipeline while keeping performance and resource use predictable.

How Logpush Transformers work

A Transformer is a SQL query written for a specific Logpush dataset. The query references fields from that dataset and defines which records and fields Logpush should export. Logpush applies the query to each batch before export. Records that do not match the WHERE clause are removed. For the remaining records, the output of the SELECT statement becomes the exported record. Transformers can change the structure and contents of each record, and the transformed results are exported in NDJSON format.

Customers can create, preview, and manage Transformers in the Cloudflare dashboard through Transformer Studio or programmatically through the API. After saving a Transformer, they can attach it to a compatible NDJSON Logpush job that uses the same dataset. Each update creates a new version, so customers can review how a Transformer has changed over time.

The following example reshapes a Cloudflare HTTP request log to match a team-defined schema used across CDN providers. It does not convert between serialization formats: both the input and output use NDJSON.

The Transformer renames and nests fields, redacts part of the client IP address, adds provider and error information, removes unused fields, and filters out internal and health-check traffic:

The resulting NDJSON record uses the normalized schema:

How Transformers executes SQL with Apache DataFusion and Arrow

Cloudflare's data pipeline ingests more than one billion events per second. Its Logpush delivery service, which we call Bufstream, delivers more than 110 million Logpush records per second to customer destinations. It runs across hundreds of Kubernetes pods, each claiming a time slice of data from Buftee, Cloudflare's distributed log-based in-house message broker. This model distributes work horizontally across Logpush jobs. Job volume follows a Pareto-like distribution: most jobs operate at lower volumes, while a small number of high-volume jobs process millions of logs each second. Transformers needed to meet the same operational requirements as the rest of Logpush: reliable delivery, high throughput, and predictable resource use without introducing additional failure scenarios into the export hot path.

Our initial prototype ran customer-defined WebAssembly Transformers in Cloudflare Workers, which provides globally distributed, isolated compute. However, invoking a Worker would insert a network call into the Logpush export path. That remote dependency could introduce transient timeouts and retries, reducing delivery throughput and increasing delivery latency.

We decided to keep Transformer execution in-process within our delivery service to prioritize reliability and delivery throughput. We evaluated several SQL execution engines and selected Apache DataFusion, which already powers Cloudflare Basin.

Apache DataFusion is a Rust query engine built on Apache Arrow, with a SQL planner and vectorized, columnar execution engine. In a benchmark, executing a prepared Transformer against a synthetic 5,000-row http_requests batch from a single Go goroutine took about 3 ms, equivalent to roughly 1.6 million rows per second.

Attaching a Transformer to a job adds CPU work to its processing path. Bufstream uses per-job transform parallelism so high-volume jobs can execute transform batches concurrently. Embedding DataFusion in Bufstream lets those batches use the service's existing delivery infrastructure, including its scheduling, batching, and destination controls, without introducing a separate transformation tier or network hop.

Choosing DataFusion meant connecting Bufstream, which is written in Go, to an engine written in Rust. The next challenge was moving typed batches efficiently across that boundary.

The final design of the in-process Transformer pipeline is shown in the diagram below.

From records to columns

Bufstream receives compressed Logpush batches containing Cap'n Proto records from Buftee. For a job with a Transformer attached, Bufstream decompresses the batch, parses the eligible logs, and builds a typed Apache Arrow RecordBatch before executing the transform.

Apache Arrow is a language-independent, columnar in-memory format designed for efficient analytics on modern CPUs and GPUs. It represents flat and nested data as typed, contiguous columns. Arrow IPC gives Bufstream and DataFusion a standard way to exchange batches across the foreign function interface (FFI) boundary between Go and Rust, exposed through a C application binary interface (ABI) and called from Go using

, Go's mechanism for calling C code.

The Go and Rust runtimes do not share ownership of transform data. Go passes a pointer to its input Arrow IPC buffer to Rust only for the duration of the cgo call, and Rust does not retain that pointer after returning. Rust owns the transformed output buffer; Go copies it into Go-managed memory and then explicitly releases the Rust allocation. This makes ownership and lifetimes explicit across the language boundary, avoiding cross-runtime memory-management bugs.

Using Arrow IPC means the Rust DataFusion wrapper can use an Arrow StreamReader to read typed RecordBatch values, rather than parse individual rows from an intermediate format such as JSON and rebuild typed Arrow columns for execution. Field types, nullability, and nested values are represented consistently on both sides of the boundary, so DataFusion receives data in its native columnar model.

Crossing the Go/Rust boundary is not free: batches still need to be serialized, decoded, and managed in memory. Arrow IPC keeps that work batch-oriented and avoids per-record parsing and conversion. This makes the boundary a better fit for Logpush's high-throughput delivery pipeline while retaining schema validation against the Logpush dataset definition.

Every Arrow batch needs a schema describing its fields and types. Rather than infer that schema from the logs in a particular batch, Bufstream supplies a generated schema from each Logpush dataset's specification. This gives DataFusion a stable view of the available fields and types, enabling query validation. The table named in a Transformer's FROM clause selects which dataset schema the query uses. For example, this Transformer queries the http_requests dataset:

Executing the transform

When a customer saves a Transformer through the API or Transformer Studio, Cloudflare stores its SQL query in R2. Bufstream retrieves the query through a multi-layer cache and translates it into a reusable DataFusion logical plan that defines the scan, filters, projections, and expressions. Bufstream prepares this plan once per time slice of a job's data and reuses it for every Arrow batch in that slice. For every new Arrow batch, the Rust wrapper binds the batch as the plan’s table input, executes the query, and returns Arrow batches containing the selected records and fields.

Transformers are designed to fail closed. If a transform cannot be executed, Bufstream neither advances the job's delivery offset nor sends the untransformed batch. Delivering raw data in place of transformed data could violate the schema, filtering, or redaction assumptions of downstream pipelines, so Bufstream opts to re-attempt failed transforms instead.

To prevent a persistently failing job from consuming capacity needed by healthy jobs, Bufstream progressively delays retries and reports errors on the job. Jobs that remain in a failing state for an extended period are automatically disabled. Customers can monitor successful and failed transformations, data volume before and after transformation, and transformation duration in the Transformer Health view of the Health tab in Logpush.

Returning to the export pipeline

After execution, Bufstream converts the Arrow output into NDJSON logs. It batches, gzip-compresses, and uploads those logs to the configured destination. Destinations accept data at different rates and can temporarily slow down. Bufstream adjusts the number of upload goroutines while respecting destination concurrency limits.

By embedding SQL execution in Bufstream, Transformers use Logpush’s existing distributed infrastructure, batching, and destination controls. Cloudflare’s data pipeline handles that complexity, while customers create and apply a Transformer with only a few steps.

Get started

Open Transformer Studio from the Logpush page in the Cloudflare dashboard and follow these steps:

• Choose the Logpush dataset you want to transform.
• Write your SQL query and preview it against a sample record.
• Save the Transformer.
• Attach it to a matching Logpush job.

Transformers is available on Free, Pro, Business, and Enterprise plans. See the Transformers documentation for setup details and the Logpush pricing documentation for current pricing information.