Resolve "Document product integration for integrating with database"

docs/developer/package-integration/package-integration-database.md

 # Big Bang Package: Database Integration
 
-If the package you are integrating connects to a database or cache server, you will need to follow the instructions below to integrate this feature into Big Bang
+If the package you are integrating connects to a database, you will need to follow the instructions below to integrate this feature into Big Bang.
 
 ## Prerequisites
 
-TBD
+- Existing database
 
 ## Integration
 
+There are currently 2 typical ways in bigbang that packages connect to a database.
+
+1. Package charts accept values for host, user, pass, etc and the chart makes the necessary secret, configmap etc.
+
+2. Package chart accepts a secret name where all the DB connection info is defined. In these cases we make the secret in the BB chart.
+
+Both ways will first require the following step:
+
+Add database values for the package in bigbang/chart/values.yaml
+
+  Note: Names of key/values may differ based on the application being integrated. Please refer to package chart values to ensure key/values coincide and application documentation for additional information on connecting to a database.
+
+```yml
+<package>
+  database:
+    # -- Hostname of a pre-existing PostgreSQL database to use.
+    host: ""
+    # -- Port of a pre-existing PostgreSQL database to use.
+    port: ""
+    # -- Database name to connect to on host.
+    database: ""
+    # -- Username to connect as to external database, the user must have all privileges on the database.
+    username: ""
+    # -- Database password for the username used to connect to the existing database.
+    password: ""
+```
+Example: [Anchore](https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/10d43bea9351b91dfc6f14d3b0c2b2a60fe60c6a/chart/values.yaml#L882)
+
+**Next details the first way packages connect to a pre-existing database.**
+
+1. Package charts accept values for host, user, pass, etc and the chart makes the necessary secret, configmap etc...
+
+- add a conditional statement to `bigbang/chart/templates/<package>/values` that will check if the database values exist and creates the necessary postgresql values.
+
+  If database values are present, then the internal database is disabled by setting `enabled: false` and the server, database, username, and port values are set.
+
+  If database values are NOT present then the internal database is enabled and default values declared in the package are used.
+
+```yml
+# External Postgres config
+{{- with .Values.<package>.database }}
+postgresql:
+  {{- if and .host .username .password .database .port }}
+  # Use external database
+  enabled: false
+  postgresqlServer: {{ .host }}
+  postgresqlDatabase: {{ .database }}
+  postgresqlUsername: {{ .username }}
+  service:
+    port: {{ .port }}
+  {{- else }}
+  # Use internal database, defaults are fine
+  enabled: true
+  {{- end }}
+{{- end }}
+```
+Example: [Anchore](https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/10d43bea9351b91dfc6f14d3b0c2b2a60fe60c6a/chart/templates/anchore/values.yaml#L49)
+
+**The alternative way packages connect to a pre-existing database is detailed below.**
+
+2. Package chart accepts a secret name where all the DB connection info is defined. In these cases we make the secret in the BB chart..
+
+- add conditional statement in `chart/templates/<package>/values.yaml` to add values for database secret, if database values exist. Otherwise the internal database is deployed.
+```yml
+{{- with .Values.addons.<package>.database }}
+{{- if and .username .password .host .port .database }}
+database:
+  secret: "<package>-database-secret"
+{{- else }}
+postgresql:
+  image:
+    pullSecrets:
+      - private-registry
+  install: true
+{{- end }}
+{{- end }}
+```
+
+Example: [Mattermost](https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/10d43bea9351b91dfc6f14d3b0c2b2a60fe60c6a/chart/templates/mattermost/mattermost/values.yaml#L49)
+
+
+- create manifest that uses database values to create the database secret referenced above
+
+```yml
+{{- if .Values.addons.<package>.enabled }}
+{{- with .Values.addons.<package>.database }}
+{{- if and .username .password .host .port .database }}
+apiVersion: v1
+kind: Secret
+type: Opaque
+metadata:
+  name: <package>-database-secret
+  namespace: <package>
+  labels:
+    {{- include "commonLabels" $ | nindent 4}}
+stringData:
+  DB_CONNECTION_CHECK_URL: "postgres://{{ .username }}:{{ .password }}@{{ .host }}:{{ .port }}/{{ .database }}?connect_timeout=10&sslmode={{ .ssl_mode | default "disable" }}"
+  DB_CONNECTION_STRING: "postgres://{{ .username }}:{{ .password }}@{{ .host }}:{{ .port }}/{{ .database }}?connect_timeout=10&sslmode={{ .ssl_mode | default "disable" }}"
+{{- end }}
+{{- end }}
+{{- end }}
+```
+
+Example: [Mattermost](https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/10d43bea9351b91dfc6f14d3b0c2b2a60fe60c6a/chart/templates/mattermost/mattermost/secret-database.yaml)
+
 ## Validation
+
+For validating connection to the external database in your environment or testing in CI pipeline you will need to add the database specific values to your overrides file or `tests/ci/k3d/values.yaml` respectively.
+
+Mattermost Example:
+
+```yml
+addons:
+  mattermost:
+    enabled: true
+    database:
+      host: "mm-postgres.bigbang.dev"
+      port: "5432"
+      username: "admin"
+      password: "Pa55w0rd"
+      database: "db1
+```