Add blog post about the OTTL context inference feature

content/en/blog/2025/ottl-contexts-just-got-easier.md

@@ -0,0 +1,155 @@
+---
+title: OTTL contexts just got easier with context inference
+linkTitle: OTTL contexts just got easier
+date: 2025-02-20
+author: '[Edmo Vamerlatti Costa](https://github.com/edmocosta) (Elastic)'
+issue: 6289
+sig: Collector SIG
+cSpell:ignore: OTTL Vamerlatti
+---
+
+Selecting the right OTTL context for running statements can be challenging, even
+for experienced users. Choosing the correct option impacts both accuracy and
+efficiency, as using higher-level OTTL contexts can avoid unnecessary iterations
+through nested lower-level contexts.
+
+To simplify this process, the OpenTelemetry community is excited to announce
+OTTL
+[context inference](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/transformprocessor/README.md#context-inference)
+support for the
+[transform processor](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/transformprocessor).
+This feature removes the need for users to understand the underlying context
+concept of OTTL, allowing them to focus solely on their data. It also improves
+statement processing efficiency by automatically selecting the most appropriate
+OTTL context. This optimization ensures that data transformations are both
+accurate and performant.
+
+## How does it work?
+
+Starting with version `0.120.0`, the transform processor supports two new
+context-inferred configuration styles. The first one offers a simpler and
+flatter approach, while the second closely resembles the existing configuration
+format.
+
+### Basic configuration
+
+The
+[basic configuration](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/transformprocessor/README.md#basic-config)
+style simplifies configuration by allowing users to list all statements
+together, without worrying about OTTL contexts or extra configuration
+structures. This style support statements from multiple OTTL contexts and does
+not require grouping them separately.
+
+To illustrate this, compare the following configuration:
+
+```yaml
+metric_statements:
+  - context: resource
+    statements:
+      - keep_keys(attributes, ["host.name"])
+  - context: metric
+    statements:
+      - set(description, "Sum") where type == "Sum"
+      - convert_sum_to_gauge() where name == "system.processes.count"
+  - context: datapoint
+    statements:
+      - limit(attributes, 100, ["host.name"])
+```
+
+With the new basic configuration style, the same logic is expressed more
+concisely by simply providing a list of statements:
+
+```yaml
+metric_statements:
+  - keep_keys(resource.attributes, ["host.name"])
+  - set(metric.description, "Sum") where metric.type == "Sum"
+  - convert_sum_to_gauge() where metric.name == "system.processes.count"
+  - limit(datapoint.attributes, 100, ["host.name"])
+```
+
+This streamlined approach enhances readability and makes configuration more
+intuitive. To use this configuration style, all paths in the statements must be
+prefixed with their respective OTTL contexts. These prefixes are required for
+all context-inferred configurations and serve as hints for selecting the best
+match. It also makes statements unambiguous and portable between components
+using OTTL.
+
+### Advanced configuration
+
+The context-inferred
+[advanced configuration](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/transformprocessor/README.md#advanced-config)
+style closely resembles the existing format and allows users to leverage the
+benefits of context inference while providing granular control over statement
+configurations, such as `error_mode` and `conditions`. For example, consider the
+following configuration:
+
+<!-- prettier-ignore-start -->
+```yaml
+metric_statements:
+  - context: datapoint
+    conditions:
+      - resource.attributes["service.name"] == "my.service"
+    statements:
+      - set(metric.description, "counter") where attributes["my.attr"] == "some"
+```
+<!-- prettier-ignore-end -->
+
+The above can now be written as:
+
+<!-- prettier-ignore-start -->
+```yaml
+metric_statements:
+  - conditions:
+      - resource.attributes["service.name"] == "my.service"
+    statements:
+      - set(metric.description, "counter") where datapoint.attributes["my.attr"] == "some"
+```
+<!-- prettier-ignore-end -->
+
+In this example, the `context` value is omitted and is automatically inferred to
+`datapoint`, as it is the only OTTL context present in the statements that
+supports parsing both `datapoint` and `metric` data.
+
+If we update the above configuration removing the `datapoint` usage:
+
+<!-- prettier-ignore-start -->
+```yaml
+metric_statements:
+  - conditions:
+      - resource.attributes["service.name"] == "my.service"
+    statements:
+      - set(metric.description, "counter")
+```
+<!-- prettier-ignore-end -->
+
+The context inferrer would select the `metric` OTTL context instead, since no
+data points are accessed. Although it would be possible to run the statements
+using the `datapoint` OTTL context, `metric` is the most efficient option.
+
+### Which configuration style should I choose?
+
+The [basic configuration](#basic-configuration) style is best suited for
+scenarios where simplicity and ease of use are paramount. It is ideal for simple
+use cases where your configuration needs are straightforward and do not require
+the use of additional configurations keys, allowing you to quickly set up your
+statements with minimal effort and without needing to understand the underlying
+concept of OTTL contexts.
+
+The [advanced configuration](#advanced-configuration) style is more detailed and
+allows the use of additional configuration keys such as `error_mode` and
+`conditions`. It supports statements from multiple OTTL contexts. However,
+unlike the basic configuration style, it may require splitting them into
+separate configuration groups (see
+[advanced config](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/processor/transformprocessor#advanced-config)).
+In terms of performance, the advanced configuration is slightly faster than the
+basic configuration, making it a better choice for complex scenarios or
+configurations with a high number of statements.
+
+## Try it out
+
+As we wrap up, we encourage users to explore this new functionality and take
+advantage of its benefits in their telemetry pipelines!
+
+If you have any questions or suggestions, we’d love to hear from you! Join the
+conversation in the `#otel-collector` channel on the
+[CNCF Slack workspace](https://slack.cncf.io/).

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