diff --git a/openapi-spec.yml b/openapi-spec.yml
index 584ad74..5ef34ec 100644
--- a/openapi-spec.yml
+++ b/openapi-spec.yml
@@ -1,6 +1,6 @@
 openapi: "3.0.0"
 info:
-  version: 0.5.0
+  version: 0.5.1
   title: xOpera API
   license:
     name: Apache-2.0
@@ -102,6 +102,26 @@ paths:
                 $ref: "#/components/schemas/DeploymentOutput"
         "404":
           description: No outputs exist for this deployment.
+  /update:
+    post:
+      summary: Do an update
+      operationId: update
+      requestBody:
+        description: Update inputs
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/UpdateRequest"
+      responses:
+        "202":
+          description: Update successfully initiated.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/Invocation"
+        "500":
+          description: There was an error initiating the update.
   /validate:
     post:
       deprecated: true
@@ -424,6 +444,7 @@ components:
         - deploy
         - undeploy
         - notify
+        - update
     OperationSuccess:
       description: A general success message.
       type: object
@@ -472,3 +493,16 @@ components:
           type: string
         csar:
           type: string
+    UpdateRequest:
+      description: Update request.
+      type: object
+      required:
+        - inputs
+        - newServiceTemplateContents
+      properties:
+        inputs:
+          type: object
+        newServiceTemplateContents:
+          description: The contents of the new service template.
+          type: string
+          format: bytes
diff --git a/src/opera/api/controllers/background_invocation.py b/src/opera/api/controllers/background_invocation.py
index 31d680e..25015f1 100644
--- a/src/opera/api/controllers/background_invocation.py
+++ b/src/opera/api/controllers/background_invocation.py
@@ -9,8 +9,12 @@
 from typing import List, Optional
 
 from opera.commands.deploy import deploy_service_template as opera_deploy
+from opera.commands.diff import diff_instances as opera_diff_instances
 from opera.commands.notify import notify as opera_notify
 from opera.commands.undeploy import undeploy as opera_undeploy
+from opera.commands.update import update as opera_update
+from opera.compare.instance_comparer import InstanceComparer
+from opera.compare.template_comparer import TemplateComparer
 from opera.storage import Storage
 
 from opera.api.log import get_logger
@@ -53,6 +57,8 @@ def _run_internal(work_queue: multiprocessing.Queue):
                 elif inv.operation == OperationType.NOTIFY:
                     # we abuse service_template and inputs a bit, but they match
                     InvocationWorkerProcess._notify(inv.service_template, inv.inputs)
+                elif inv.operation == OperationType.DEPLOY:
+                    InvocationWorkerProcess._update(inv.service_template, inv.inputs, num_workers=1)
                 else:
                     raise RuntimeError("Unknown operation type:" + str(inv.operation))
 
@@ -95,6 +101,24 @@ def _notify(event_name: str, notification_contents: Optional[str]):
         opera_notify(opera_storage, verbose_mode=True,
                      trigger_name_or_event=event_name, notification_file_contents=notification_contents)
 
+    @staticmethod
+    def _update(service_template: str, inputs: typing.Optional[dict], num_workers: int):
+        original_storage = Storage.create()
+
+        new_storage = Storage.create(instance_path=".opera-api-update")
+        new_storage.write_json(inputs, "inputs")
+        new_storage.write(service_template, "root_file")
+
+        instance_diff = opera_diff_instances(
+            original_storage, ".", new_storage, ".",
+            TemplateComparer(), InstanceComparer(), True
+        )
+
+        opera_update(
+            original_storage, ".", new_storage, ".",
+            InstanceComparer(), instance_diff, True, num_workers, overwrite=True
+        )
+
     @staticmethod
     def read_file(filename):
         with open(filename, "r") as f:
diff --git a/src/opera/api/controllers/default.py b/src/opera/api/controllers/default.py
index d42a59b..220b5e6 100644
--- a/src/opera/api/controllers/default.py
+++ b/src/opera/api/controllers/default.py
@@ -1,5 +1,6 @@
 import tempfile
 import traceback
+from datetime import datetime
 from pathlib import PurePath
 
 from opera.commands.diff import diff_instances as opera_diff_instances
@@ -18,7 +19,7 @@
 from opera.api.controllers.background_invocation import InvocationService
 from opera.api.log import get_logger
 from opera.api.openapi.models import ValidationResult, OperationType, CsarInitializationInput, PackagingInput, \
-    UnpackagingInput, PackagingResult, Info, CsarValidationInput, DiffRequest, Diff
+    UnpackagingInput, PackagingResult, Info, CsarValidationInput, DiffRequest, Diff, UpdateRequest
 from opera.api.openapi.models.deployment_input import DeploymentInput
 
 logger = get_logger(__name__)
@@ -33,7 +34,7 @@ def deploy(body: DeploymentInput = None):
     deployment_input = DeploymentInput.from_dict(body)
     result = invocation_service.invoke(OperationType.DEPLOY, deployment_input.service_template,
                                        deployment_input.inputs, deployment_input.clean_state)
-    return result, 200
+    return result, 202
 
 
 def diff(body: dict = None):
@@ -208,3 +209,17 @@ def unpackage(unpackaging_input: UnpackagingInput):
         return {"success": True, "message": ""}, 200
     except Exception as e:
         return {"success": False, "message": "General error: {}".format(str(e))}, 500
+
+
+def update(body: dict = None):  # noqa: E501
+    logger.debug("Entry: update")
+    update_request = UpdateRequest.from_dict(body)
+
+    posixnow = int(datetime.utcnow().timestamp())
+    with open("st-operaapi-update-{}.yml".format(posixnow)) as new_st_file:
+        new_st_file.write(update_request.new_service_template_contents)
+        new_st_filename = new_st_file.name
+
+    result = invocation_service.invoke(OperationType.UPDATE, new_st_filename, update_request.inputs, False)
+
+    return result, 202