feat(prefect-server): support sqlite database (#418)

* feat(prefect-server): support sqlite database Supports using sqlite for the database in place of postgresql. Closes https://linear.app/prefect/issue/PLA-139/support-sqlite-database * Disable hpa, secret if sqlite enabled - HPA is not desired given that sqlite requires 1 replica - secret is postgresql-specific * Add tests for sqlite settings * Fix resiliency of separate test This test, separate from my changes, failed because it was looking for a volumeMount at a specific index. This change allows it to just confirm the entry is present without worrying about a specific location in the list. * Fix mount setting, hosting at /data The application was failing to start, saying it couldn't access the database file. This change mounts a directory without a subPath setting, allowing the application to create the file instead. * Make persistence settings more configurable * Add to values schema * Add documentation on enabling sqlite * Replace hard-coded PVC name Uses a template to calculate the PVC name, matching the pattern used for other objects like the Deployment.
PrefectHQ · Dec 5, 2024 · f1e9d3a · f1e9d3a
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diff --git a/charts/prefect-server/README.md b/charts/prefect-server/README.md
@@ -109,6 +109,29 @@ prefect-server:
     postgresql+asyncpg://{username}:{password}@{hostname}/{database}?ssl=verify-ca
     ```
 
+## SQLite Configuration
+
+SQLite can be used as an alternative to PostgreSQL. As mentioned in the
+[documentation on hosting Prefect](https://docs-3.prefect.io/v3/manage/self-host),
+SQLite is only recommended for lightweight, single-server deployments.
+
+To use SQLite for the database, provide the following configuration values:
+
+```yaml
+postgresql:
+  enabled: false
+sqlite:
+  enabled: true
+```
+
+More configuration options are available in [`values.yaml`](./values.yaml).
+
+By default, a PersistentVolumeClaim persists the SQLite database file between
+Pod restarts.
+
+Note that enabling SQLite enforces 1 replica in the Deployment, and disables
+the HorizontalPodAutoscaler.
+
 ## Maintainers
 
 | Name | Email | Url |
@@ -227,6 +250,10 @@ prefect-server:
 | serviceAccount.annotations | object | `{}` | additional service account annotations (evaluated as a template) |
 | serviceAccount.create | bool | `true` | specifies whether a ServiceAccount should be created |
 | serviceAccount.name | string | `""` | the name of the ServiceAccount to use. if not set and create is true, a name is generated using the common.names.fullname template |
+| sqlite.enabled | bool | `false` | enable use of the embedded SQLite database |
+| sqlite.persistence.enabled | bool | `true` | enable SQLite data persistence using PVC |
+| sqlite.persistence.size | string | `"1Gi"` | size for the PVC |
+| sqlite.persistence.storageClassName | string | `""` | storage class name for the PVC |
 
 ----------------------------------------------
 Autogenerated from chart metadata using [helm-docs v1.13.1](https://github.com/norwoodj/helm-docs/releases/v1.13.1)
diff --git a/charts/prefect-server/templates/deployment.yaml b/charts/prefect-server/templates/deployment.yaml
@@ -14,7 +14,7 @@ metadata:
   {{- end }}
 spec:
   revisionHistoryLimit: {{ .Values.server.revisionHistoryLimit }}
-  replicas: {{ .Values.server.replicaCount }}
+  replicas: {{ .Values.sqlite.enabled | ternary 1 .Values.server.replicaCount }}
   selector:
     matchLabels: {{- include "common.labels.matchLabels" . | nindent 6 }}
       app.kubernetes.io/component: server
@@ -99,10 +99,14 @@ spec:
             - name: PREFECT_UI_STATIC_DIRECTORY
               value: {{ .Values.server.uiConfig.prefectUiStaticDirectory | quote }}
             - name: PREFECT_API_DATABASE_CONNECTION_URL
+              {{- if .Values.sqlite.enabled }}
+              value: "sqlite+aiosqlite:////data/prefect.db"
+              {{- else }}
               valueFrom:
                 secretKeyRef:
                   name: {{ include "server.postgres-string-secret-name" . }}
                   key: connection-string
+              {{- end }}
             {{- if .Values.server.env }}
             {{- include "common.tplvalues.render" (dict "value" .Values.server.env "context" $) | nindent 12 }}
             {{- end }}
@@ -145,6 +149,10 @@ spec:
             - mountPath: {{ .Values.server.uiConfig.prefectUiStaticDirectory }}
               name: scratch
               subPathExpr: ui-build
+            {{- if .Values.sqlite.enabled }}
+            - mountPath: /data
+              name: sqlite-storage
+            {{- end }}
           {{- if .Values.server.extraVolumeMounts }}
           {{- include "common.tplvalues.render" (dict "value" .Values.server.extraVolumeMounts "context" $) | nindent 12 }}
           {{- end }}
@@ -154,6 +162,11 @@ spec:
       volumes:
         - name: scratch
           emptyDir: {}
+        {{- if .Values.sqlite.enabled }}
+        - name: sqlite-storage
+          persistentVolumeClaim:
+            claimName: {{ template "common.names.fullname" . }}-sqlite
+        {{- end }}
         {{- if .Values.server.extraVolumes }}
         {{- include "common.tplvalues.render" (dict "value" .Values.server.extraVolumes "context" $) | nindent 8 }}
         {{- end }}
diff --git a/charts/prefect-server/templates/hpa.yaml b/charts/prefect-server/templates/hpa.yaml
@@ -1,4 +1,4 @@
-{{- if and .Values.server.autoscaling.enabled .Values.server.resources.requests }}
+{{- if and .Values.server.autoscaling.enabled .Values.server.resources.requests (not .Values.sqlite.enabled) }}
 apiVersion: autoscaling/v2
 kind: HorizontalPodAutoscaler
 metadata:

diff --git a/charts/prefect-server/templates/pvc.yaml b/charts/prefect-server/templates/pvc.yaml
@@ -0,0 +1,16 @@
+{{- if and .Values.sqlite.enabled .Values.sqlite.persistence.enabled }}
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: {{ template "common.names.fullname" . }}-sqlite
+  namespace: {{.Release.Namespace}}
+spec:
+  {{- with .Values.sqlite.persistence.storageClassName }}
+  storageClassName: {{.}}
+  {{- end }}
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: {{.Values.sqlite.persistence.size}}
+{{- end }}
diff --git a/charts/prefect-server/templates/secret.yaml b/charts/prefect-server/templates/secret.yaml
@@ -1,4 +1,4 @@
-{{- if .Values.secret.create }}
+{{- if and  .Values.secret.create (not .Values.sqlite.enabled) }}
 apiVersion: v1
 kind: Secret
 metadata:

diff --git a/charts/prefect-server/tests/database_test.yaml b/charts/prefect-server/tests/database_test.yaml
@@ -8,6 +8,81 @@ envSecretPath: &envSecretPath .spec.template.spec.containers[?(@.name == "prefec
 defaultSecretName: &defaultSecretName prefect-server-postgresql-connection
 
 tests:
+  # SQLite embedded database tests
+
+  - it: Should correctly configure SQLite connection string
+    set:
+      postgresql:
+        enabled: false
+      sqlite:
+        enabled: true
+    asserts:
+      - template: deployment.yaml
+        contains:
+          path: .spec.template.spec.containers[0].env
+          content:
+            name: PREFECT_API_DATABASE_CONNECTION_URL
+            value: sqlite+aiosqlite:////data/prefect.db
+
+  - it: Should correctly configure SQLite storage settings
+    set:
+      postgresql:
+        enabled: false
+      sqlite:
+        enabled: true
+    asserts:
+      - template: deployment.yaml
+        contains:
+          path: .spec.template.spec.volumes
+          content:
+            name: sqlite-storage
+            persistentVolumeClaim:
+              claimName: prefect-server-sqlite
+      - template: deployment.yaml
+        contains:
+          path: .spec.template.spec.containers[0].volumeMounts
+          content:
+            mountPath: /data
+            name: sqlite-storage
+      - template: pvc.yaml
+        containsDocument:
+          kind: PersistentVolumeClaim
+          apiVersion: v1
+          name: prefect-server-sqlite
+          namespace: prefect
+
+  - it: Should not allow an HPA
+    set:
+      postgresql:
+        enabled: false
+      sqlite:
+        enabled: true
+      server:
+        autoscaling:
+          enabled: true
+    asserts:
+      - template: hpa.yaml
+        not: true
+        containsDocument:
+          apiVersion: autoscaling/v2
+          kind: HorizontalPodAutoscaler
+          name: prefect-server
+          namespace: prefect
+
+  - it: Should not allow more than 1 replica
+    set:
+      postgresql:
+        enabled: false
+      sqlite:
+        enabled: true
+      server:
+        replicaCount: 5
+    asserts:
+      - template: deployment.yaml
+        equal:
+          path: .spec.replicas
+          value: 1
+
   # Bundled PostgreSQL chart tests
 
   - it: Should produce the expected secret name and content with the defaults

diff --git a/charts/prefect-server/tests/server_test.yaml b/charts/prefect-server/tests/server_test.yaml
@@ -462,9 +462,11 @@ tests:
             mountPath: /app/config
     asserts:
       - template: deployment.yaml
-        equal:
-          path: .spec.template.spec.containers[0].volumeMounts[3].name
-          value: config
+        contains:
+          path: .spec.template.spec.containers[0].volumeMounts
+          content:
+            name: config
+            mountPath: /app/config
 
   - it: Should set extra arguments
     set:
@@ -600,4 +602,4 @@ tests:
       - template: hpa.yaml
         equal:
           path: .spec.metrics[1].resource.target.averageUtilization
-          value: 80
+          value: 80
diff --git a/charts/prefect-server/values.schema.json b/charts/prefect-server/values.schema.json
@@ -441,6 +441,42 @@
         }
       }
     },
+    "sqlite": {
+      "type": "object",
+      "title": "SQLite",
+      "description": "sqlite configuration",
+      "additionalProperties": false,
+      "properties": {
+        "enabled": {
+          "type": "boolean",
+          "title": "Enabled",
+          "description": "enable sqlite database"
+        },
+        "persistence": {
+          "type": "object",
+          "title": "Persistence",
+          "description": "persistence settings for sqlite",
+          "additionalProperties": false,
+          "properties": {
+            "enabled": {
+              "type": "boolean",
+              "title": "Enabled",
+              "description": "enable sqlite database persistence"
+            },
+            "size": {
+              "type": "string",
+              "title": "Size",
+              "description": "size of the persistent volume claim"
+            },
+            "storageClassName": {
+              "type": "string",
+              "title": "Storage class name",
+              "description": "storage class name for the persistent volume claim"
+            }
+          }
+        }
+      }
+    },
     "serviceAccount": {
       "type": "object",
       "title": "Service Account",

diff --git a/charts/prefect-server/values.yaml b/charts/prefect-server/values.yaml
@@ -315,6 +315,20 @@ secret:
   # -- database for the PostgreSQL connection string
   database: ""
 
+# SQLite configuration
+# Recommended for lightweight, single-server deployments.
+sqlite:
+  # -- enable use of the embedded SQLite database
+  enabled: false
+
+  persistence:
+    # -- enable SQLite data persistence using PVC
+    enabled: true
+    # -- size for the PVC
+    size: 1Gi
+    # -- storage class name for the PVC
+    storageClassName: ""
+
 # PostgreSQL subchart - default overrides
 postgresql:
   # -- enable use of bitnami/postgresql subchart