Topology Producers

Developer skill for assistants working in this repository, not an operator skill. It routes to the documents that own each fact and keeps only the rules and workflow that have no other owner. When you find a fact here and in an owner document, verify the affected contract at its source and correct stale guidance during authorized maintenance.

Apply AGENTS.md#skill-selection. Review the affected planes and existing design/validation evidence; authoring steps below do not require reviewers to create a SOW, redesign unrelated planes or query a live Agent. Live verification recipes apply only when the task includes that operation. A changed validator requires checking the claims it affects.

Owners

Read the owner for the plane you touch; do not work from memory of it.

If the task also changes or reviews the collector that hosts the producer, .agents/skills/collectors-authoring/SKILL.md routes that work. SNMP profile topology: rows (which OIDs feed the producer) belong to collectors-snmp-profiles; this skill starts where those rows have become observations.

Producers

All five emit netdata.topology.v1; no producer still emits a pre-v1 payload. Remaining per-producer refinements are tracked in src/plugins.d/FUNCTION_TOPOLOGY_IMPLEMENTATION_SCOPE.md#current-migration-inventory. Cross-producer fixtures live in src/go/tools/functions-validation/fixtures/topology-v1/ (none for topology:cato_networks); the Cloud aggregator itself is not in this repository.

What The Code Enforces

Use this map to locate enforcement and its known limits. Before relying on a claim affected by the task, verify it in the current schema, validator and relevant tests. Do not re-audit unrelated behavior or infer enforcement from this summary alone; distinguish intended contract from what the checked implementation actually rejects.

• JSON Schema (FUNCTION_TOPOLOGY_SCHEMA.json): structure, required fields, closed tokens, unknown properties. A violation is an error from any validator that loads the schema. It does not check cross-references or row counts.
• Go semantic validator (topologyv1.ValidateDecodedData on data, topologyv1.ValidateDecodedResponse on a whole envelope; both return an error, there is no warning level): actor and link reference bounds (evidence references only where the table type declares source_evidence), column-length equality with rows, dictionary indexes, label-policy display types, search columns and label-key shape independently of optional actor presentation, declared actor aggregation-scope memberships, the ports.sources[] rules except the actor_table carve-out below (and show_bullets is read untyped, so only the schema rejects a non-boolean), highlight-path column types (including that a path_table not under data.tables.actor is owned by actor, the one use the validator makes of table_type.owner), every overlay-refs convention rule except the id-pattern rule (schema-only), correlation rules and point/claim key columns, all modal projections, and the presentation, correlation, and overlay token vocabularies. Structural tokens (orientation, direction_role, link_type.aggregation.*, evidence_type.role, table_type.role and aggregation, column.role, layer, view.mode, supported_modes, evidence_policy) are schema-only; the Go validator never reads them. Producer tests call ValidateDecodedData (cato_networks/topology_test.go is the reference shape). The CLI tool always validates against one JSON Schema first, defaulting to FUNCTION_UI_SCHEMA.json, which rejects a topology payload, so a topology run passes --schema ../plugins.d/FUNCTION_TOPOLOGY_SCHEMA.json from src/go (src/go/tools/functions-validation/README.md#validate-topology-v1-fixtures); it then calls ValidateDecodedResponse.
• The CLI tool (src/go/tools/functions-validation) counts a topology payload's rows as max(actor rows, link rows) (topologyv1.GraphRowsFromDecodedData) for its --min-rows and --require-rows gates, so an actor-only payload passes; nothing in pkg/topology caps row counts.
• Not checked by the Go validator although the contract states them: actor_labels key, value, source, and kind column types (only actor_column is type-checked), search.label_keys[] against any label registry (string shape only), correlation key_space values (schema-required, never read), unknown optional column ids on actor_table port sources, and the owner of a detail table named as an actor_table source by port bullets, modal sections, or modal labels (a link- or evidence-owned table is accepted there).
• The network-connections 64 MiB budget is a producer-side hard stop (a 413 Function error), not a validator check (src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#network-connections-shape).
• The SNMP scenario golden suite skips, not fails, without the external fixture checkout (src/go/plugin/go.d/collector/snmp_topology/ARCHITECTURE.md#scenario-golden-suite). A green run without the skip line checked proves nothing.
• Nothing enforces: payload size on realistic data, actor identity stability across restarts, that a modal section is a recipe rather than a duplicated table, or that a type id follows the semantic conventions. Those are review items.

Workflow

Select the steps for the affected planes; a new producer considers every applicable plane. Implementation reads its owners before design, while review checks the resulting contracts and evidence. Guide means src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md.

1. Purpose and scale: name the graph users need, choose which plane carries what, and estimate actor, link, and evidence row counts and raw payload size on realistic data before choosing shapes. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#mental-model (planes), src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#producer-checklist (measure on realistic or captured fixtures).
2. Actors: stable identity, display separate from identity, identity / merge_identity / parent_identity, search, and the aggregation scopes an actor type advertises. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#required-actor-semantics; scopes and grouping: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#aggregation-rules, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#network-connections-actor-grouping.
3. Links and direction: compact renderable relationships, one-to-many detail in evidence, semantic link types per meaning, orientation plus direction_role. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#required-link-semantics.
4. Evidence and tables: lossless relationship proof versus actor-owned detail, table roles, actor_labels. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#evidence-plane, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#detail-tables, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#actor-labels-and-modal-composition.
5. Overlays: templates once, compact refs per row. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#telemetry-overlays. Go builders: topologyv1.NewActorOverlayRefsBuilder, NewLinkOverlayRefsBuilder (src/go/pkg/topology/v1); in go.d pass job.Name() as collect_job, never job.FullName() (src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#vsphere-shape).
6. Correlation: rule classes, actions, points and claims, and what the aggregator does with them. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#correlation-plane, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#aggregator-behavior.
7. Presentation and modals: type-level tokens only, label_policy, ports.sources[], highlight paths, modal recipes over existing sources; recipes in how-tos/add-graph-presentation.md. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#presentation-plane, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#closed-token-vocabulary, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#actor-labels-and-modal-composition.
8. Compact tables: const / dict / values codecs. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#compact-tables. Go builders: topologyv1.NewTableBuilder, MustTable, NewStringDictionary (src/go/pkg/topology/v1).
9. Notifications, if any: data.notifications only, origin kept separate from affected_node_id, CTS acceptance verified before Agents emit. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#notifications.
10. Per-producer contract. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#network-connections-shape, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#streaming-shape and src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#streaming-modal-sections, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#snmpl2-shape and src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#snmp-logical-l3-and-control-plane-links, src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#vsphere-shape.
11. Validate and measure: schema plus semantic validation in tests, the producer's own suites (table above), size on realistic data, and the checklist. Guide: src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#producer-checklist.

Rules Without A Code Owner

• Raw captures of real payloads stay under .local/ (repository rule, AGENTS.md). actor_labels inherits the Function's sensitive-data classification (src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#actor-labels-and-modal-composition); streaming detail tables carry node and Cloud identifiers that never become graph labels and are redacted before they reach logs, docs, SOWs, or review artifacts (src/plugins.d/FUNCTION_TOPOLOGY_DEVELOPER_GUIDE.md#streaming-shape).
• Sparse grouping columns: test that a consumer keeps actor identity for null or empty grouping keys instead of merging every null row into one bucket.
• Fail explicitly on any size or row limit; never truncate a topology and present it as complete.
• Validators need negative tests: missing label-policy columns, non-display label columns, a missing port-bullet source table, bad highlight-path columns, an invalid token, and a modal projection over a missing source. A producer that emits data.notifications tests schema and semantic parity, omission of the field, and malformed entries.
• A C producer can be syntax-checked without a full build: configure with cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON, then run the file's command from build/compile_commands.json with -fsyntax-only.
• Design the schema does not carry yet (four-dimension table merge policy, loose-side materialization) is recorded in src/plugins.d/FUNCTION_TOPOLOGY_IMPLEMENTATION_SCOPE.md#design-not-yet-in-the-schema; do not emit it and do not document it as contract.

How-Tos

• how-tos/add-graph-presentation.md: add type-level presentation, port bullets, legends, and per-actor highlight paths to a producer, with the negative tests that catch the usual mistakes.
• how-tos/preserve-semantic-link-types.md: keep protocol, confidence, and inferred state as distinct link types.
• how-tos/verify-network-connections-layout-tokens.md: check a live local Agent's link layout tokens and correlation wiring without exposing identifiers.

Capture timing and authorization follow AGENTS.md#knowledge-capture. Authorized developer recipes stay in this skill and are listed above; operator recipes belong under docs/netdata-ai/skills/.