feature: #146 add database discovery receiver

.gitattributes

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+# Normalize and enforce LF line endings for all text files
+* text=auto eol=lf

CHANGELOG.md

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 ## vNext
 - Updates golang to 1.25.1
+- Added receiver `swok8sdiscovery` to publish known database entities and relationships
 
 ## v0.131.8
 - `solarwindsprocessor` Refactored collector decoration configuration: introduced `collector_attributes_decoration` section with `enabled` and `extension` fields, deprecated root-level `extension` field for better configuration organization

receiver/swok8sdiscovery/Makefile

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+include ../../Makefile.Common

receiver/swok8sdiscovery/README.md

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+## swok8sdiscovery Receiver
+
+| Status        |           |
+| ------------- |-----------|
+| Stability     | [alpha]: logs   |
+| Distributions | [k8s] |
+| Issues        | [![Open issues](https://img.shields.io/github/issues-search/solarwinds/solarwinds-otel-collector-contrib?query=is%3Aissue%20is%3Aopen%20label%3Areceiver%2Fswok8sdiscovery%20&label=open&color=orange&logo=opentelemetry)](https://github.com/solarwinds/solarwinds-otel-collector-contrib/issues?q=is%3Aopen+is%3Aissue+label%3Areceiver%2Fswok8sdiscovery) [![Closed issues](https://img.shields.io/github/issues-search/solarwinds/solarwinds-otel-collector-contrib?query=is%3Aissue%20is%3Aclosed%20label%3Areceiver%2Fswok8sdiscovery%20&label=closed&color=blue&logo=opentelemetry)](https://github.com/solarwinds/solarwinds-otel-collector-contrib/issues?q=is%3Aclosed+is%3Aissue+label%3Areceiver%2Fswok8sdiscovery) |
+
+[alpha]: https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/component-stability.md#alpha
+[k8s]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-k8s
+
+
+
+The `swok8sdiscovery` receiver performs periodic discovery of databases used in a Kubernetes cluster and emits **entity events as OpenTelemetry log records** describing discovered database instances and their relationships to owning Kubernetes workloads (Deployment / StatefulSet / DaemonSet / Job / CronJob).
+
+Discovery currently supports two complementary strategies (both optional – enable either or both):
+
+1. Image-based discovery (`database.image_rules`):
+	 - Matches container image names against user-provided regular expressions.
+	 - Optionally constrains to a single default port when specified.
+	 - Resolves a stable endpoint using the best matching Service (selector overlaps chosen ports) or falls back to the Pod name.
+2. Domain-based discovery (`database.domain_rules`):
+	 - Matches `ExternalName` Services whose external DNS name matches configured patterns.
+	 - When multiple rules match, the one whose `database_type` or any of its `domain_hints` appears in either the service name or external domain is preferred.
+
+Each discovered database produces:
+* An entity state log (type = `entity_state`) with attributes under `otel.entity.id` identifying the database (`sw.discovery.dbo.address`, `sw.discovery.dbo.type`, `sw.discovery.id`).
+* (If workload ownership resolved) A relationship log (type = `entity_relationship_state`) linking the database entity to a Kubernetes workload (relation type `DiscoveredBy`).
+
+### Emitted Attributes (selection)
+| Attribute | Description |
+|-----------|-------------|
+| `otel.entity.event.type` | `entity_state` or `entity_relationship_state` |
+| `otel.entity.type` | Always `DiscoveredDatabaseInstance` for entity events |
+| `sw.discovery.dbo.address` | Endpoint + (resolved) port list, e.g. `mongo-svc:27017` |
+| `sw.discovery.dbo.type` | Logical database type (e.g. `mongo`, `postgres`, `redis`) |
+| `sw.discovery.dbo.name` | Endpoint plus workload name (`<endpoint>#<workload>`) when workload present |
+| `sw.discovery.source` | Value of configured `reporter` (for provenance) |
+| `k8s.<workload kind>.name` | Name of owning workload (when resolved) |
+| `k8s.namespace.name` | Namespace of the workload/pod/service |
+| `sw.k8s.cluster.uid` | Cluster UID (from environment `CLUSTER_UID`) |
+
+### Configuration
+
+Top-level settings:
+
+| Field | Type | Default | Description |
+|-------|------|---------|-------------|
+| `interval` | duration | `5m` | Time between discovery cycles. Shorten in tests (e.g. `15s`). |
+| `reporter` | string | empty | Optional source label recorded as `sw.discovery.source`. |
+| `k8s` auth fields | (inlined via `APIConfig`) | | Standard Kubernetes client auth (service account, kubeconfig, etc.). |
+| `database` | object | nil | Enables database discovery if provided. |
+
+`database.image_rules` entries:
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `database_type` | string | yes | Logical database type label. |
+| `patterns` | []string (regex) | yes | Regex patterns matched against full container image (e.g. `docker.io/library/mongo:.*`). |
+| `default_port` | int | no | If present and exists among container ports, only that port will be emitted (deduping multi-port images). |
+
+`database.domain_rules` entries:
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `database_type` | string | yes | Logical database type label. |
+| `patterns` | []string (regex) | yes | Patterns matched against `ExternalName` value. |
+| `domain_hints` | []string | no | Tie-break hints (substring matches in service name or external domain). |
+
+### Example Configuration
+
+```yaml
+receivers:
+	swok8sdiscovery:
+		interval: 30s
+		reporter: "agent"
+		# Kubernetes auth (service account in-cluster example)
+		auth_type: serviceAccount
+		database:
+			image_rules:
+				- database_type: mongo
+					patterns: [".*/mongo:.*"]
+					default_port: 27017
+				- database_type: postgres
+					patterns: [".*/postgres:.*"]
+					default_port: 5432
+			domain_rules:
+				- database_type: redis
+					patterns: [".*redis.example.com"]
+
+exporters:
+	debug:
+		verbosity: detailed
+
+service:
+	pipelines:
+		logs:
+			receivers: [swok8sdiscovery]
+			exporters: [debug]
+```

receiver/swok8sdiscovery/config.go

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+// Copyright 2025 SolarWinds Worldwide, LLC. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package swok8sdiscovery
+
+import (
+	"context"
+	"errors"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/solarwinds/solarwinds-otel-collector-contrib/internal/k8sconfig"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	k8s "k8s.io/client-go/kubernetes"
+)
+
+const (
+	defaultInterval time.Duration = time.Minute * 5
+)
+
+type Config struct {
+	k8sconfig.APIConfig `mapstructure:",squash"`
+
+	Interval time.Duration `mapstructure:"interval"`
+
+	Reporter string `mapstructure:"reporter"`
+
+	Database *DatabaseDiscoveryConfig `mapstructure:"database"`
+
+	// For mocking purposes only.
+	makeClient func() (k8s.Interface, error)
+}
+
+type DatabaseDiscoveryConfig struct {
+	ImageRules  []*ImageRule  `mapstructure:"image_rules"`
+	DomainRules []*DomainRule `mapstructure:"domain_rules"`
+}
+
+type ImageRule struct {
+	DatabaseType string `mapstructure:"database_type"`
+	// regular expressions patterns to match against container images
+	Patterns         []string         `mapstructure:"patterns"`
+	PatternsCompiled []*regexp.Regexp `mapstructure:"-"` // compiled from Patterns during validation
+
+	// default port for database communitation if not specified elsewhere
+	DefaultPort int32 `mapstructure:"default_port"`
+}
+
+type DomainRule struct {
+	DatabaseType string `mapstructure:"database_type"`
+	// communication endpoint must match at least one of these patterns
+	Patterns         []string         `mapstructure:"patterns"`
+	PatternsCompiled []*regexp.Regexp `mapstructure:"-"` // compiled from Patterns during validation
+
+	// in case more DomainRules match, this one will be preferred to be found in service name or endpoint self
+	DomainHints []string `mapstructure:"domain_hints"`
+}
+
+func (c *Config) Validate() error {
+	if err := c.APIConfig.Validate(); err != nil {
+		return err
+	}
+
+	if c.Interval == 0 {
+		c.Interval = defaultInterval
+	}
+
+	// validate that rules doesn't have databaseType empty
+	if c.Database != nil {
+		if err := ValidateDatabaseDiscovery(c.Database); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func ValidateDatabaseDiscovery(databaseDiscovery *DatabaseDiscoveryConfig) error {
+	for i := range databaseDiscovery.ImageRules {
+		r := databaseDiscovery.ImageRules[i]
+		if r.DatabaseType == "" {
+			return errors.New("database_type must be specified for all image_rules")
+		}
+		r.DatabaseType = strings.ToLower(r.DatabaseType)
+
+		if len(r.Patterns) == 0 {
+			return errors.New("at least one match pattern must be specified for all image_rules")
+		}
+
+		r.PatternsCompiled = make([]*regexp.Regexp, len(r.Patterns))
+		for j, pattern := range r.Patterns {
+			compiled, err := regexp.Compile(pattern)
+			if err != nil {
+				return err
+			}
+			r.PatternsCompiled[j] = compiled
+		}
+	}
+
+	for i := range databaseDiscovery.DomainRules {
+		r := databaseDiscovery.DomainRules[i]
+		if r.DatabaseType == "" {
+			return errors.New("database_type must be specified for all domain_rules")
+		}
+		r.DatabaseType = strings.ToLower(r.DatabaseType)
+		if len(r.Patterns) == 0 {
+			return errors.New("at least one match pattern must be specified for all domain_rules")
+		}
+
+		r.PatternsCompiled = make([]*regexp.Regexp, len(r.Patterns))
+		for j, pattern := range r.Patterns {
+			compiled, err := regexp.Compile(pattern)
+			if err != nil {
+				return err
+			}
+			r.PatternsCompiled[j] = compiled
+		}
+
+		for j, hint := range r.DomainHints {
+			r.DomainHints[j] = strings.ToLower(hint)
+		}
+	}
+	return nil
+}
+
+func (c *Config) getClient() (k8s.Interface, error) {
+	if c.makeClient != nil {
+		return c.makeClient()
+	}
+	return k8sconfig.MakeClient(c.APIConfig)
+}
+
+// listPods lists all pods across all namespaces using the typed client.
+func (c *Config) listPods(ctx context.Context, client k8s.Interface) ([]corev1.Pod, error) {
+	pl, err := client.CoreV1().Pods(metav1.NamespaceAll).List(ctx, metav1.ListOptions{})
+	if err != nil {
+		return nil, err
+	}
+	return pl.Items, nil
+}
+
+// listServices lists all services across all namespaces using the typed client.
+func (c *Config) listServices(ctx context.Context, client k8s.Interface) ([]corev1.Service, error) {
+	sl, err := client.CoreV1().Services(metav1.NamespaceAll).List(ctx, metav1.ListOptions{})
+	if err != nil {
+		return nil, err
+	}
+	return sl.Items, nil
+}