---
title: Dry Run
---
The dry run feature is a very useful way to check the correctness of the application configuration and definitions. It will render the application and print the output resources that checked on the service side. If the definitions(component, trait) is invalid, the dry run will print the error message.
When you do the following things, you'd better use `dry-run`.
* Create or update an application.
* Create or update the definition, and dry run some example applications.
## Dry run via CLI
There is a simple application:
```yaml
kind: Application
apiVersion: core.oam.dev/v1beta1
metadata:
name: webservice-app
spec:
components:
- name: frontend
type: webservice
properties:
image: oamdev/testapp:v1
cmd: ["node", "server.js"]
ports:
- port: 8080
expose: true
traits:
- type: scaler
properties:
replicas: 1
```
Copy it and write a file `app.yaml`, execute the following command, and then the resources will be printed.
```bash
vela dry-run app.yaml
```
expected output
```yaml
---
# Application(webservice-app) -- Component(frontend)
---
apiVersion: apps/v1
kind: Deployment
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: frontend
app.oam.dev/name: webservice-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: WORKLOAD
workload.oam.dev/type: webservice
name: frontend
namespace: default
spec:
replicas: 1
selector:
matchLabels:
app.oam.dev/component: frontend
template:
metadata:
labels:
app.oam.dev/component: frontend
app.oam.dev/name: webservice-app
spec:
containers:
- command:
- node
- server.js
image: oamdev/testapp:v1
name: frontend
ports:
- containerPort: 8080
name: port-8080
protocol: TCP
---
## From the auxiliary workload
apiVersion: v1
kind: Service
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: frontend
app.oam.dev/name: webservice-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: TRAIT
trait.oam.dev/resource: webserviceExpose
trait.oam.dev/type: AuxiliaryWorkload
name: frontend
namespace: default
spec:
ports:
- name: port-8080
port: 8080
targetPort: 8080
selector:
app.oam.dev/component: frontend
type: ClusterIP
---
```
If we set the expose field of the port as false, the output resources do not include the `Service`. If we set the replicas field as "1", the output will be an error message:
```bash
Error: validate application: ./app.yaml by dry-run: admission webhook "validating.core.oam.dev.v1beta1.applications" denied the request: field "schematic": Invalid value error encountered, cannot evaluate trait "scaler": invalid template of trait scaler after merge with parameter and context: parameter.replicas: conflicting values (*1 | int) and "1" (mismatched types int and string) (and 1 more errors).
```
This means the replicas field is int type but we provide a string value, this application configuration is not valid.
### Dry run with policy and workflow via CLI
:::tip
Override/topology Policies and deploy workflow are supported in v1.7.0+ now. While there're still some limitation that `dry-run` with policy and workflow will only take `override`, `topology` policies and `deploy` workflow step into considerations. Other workflow steps will be ignored.
:::
Let's take the following application as example, the application explicitly specify `override`, `topology` policies and `deploy` workflow step.
```yaml
apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: first-vela-app
spec:
components:
- name: express-server
type: webservice
properties:
image: oamdev/hello-world
ports:
- port: 8000
expose: true
traits:
- type: scaler
properties:
replicas: 1
policies:
- name: target-default
type: topology
properties:
clusters: ["local"]
namespace: "default"
- name: target-prod
type: topology
properties:
clusters: ["local"]
namespace: "prod"
- name: deploy-ha
type: override
properties:
components:
- type: webservice
traits:
- type: scaler
properties:
replicas: 5
workflow:
steps:
- name: deploy2default
type: deploy
properties:
policies: ["target-default"]
- name: manual-approval
type: suspend
- name: deploy2prod
type: deploy
properties:
policies: ["target-prod", "deploy-ha"]
```
Dry run will produce rendered results for both `deploy2default` and `deploy2prod` deploy steps as below:
expected output
```yaml
---
# Application(first-vela-app with topology target-default) -- Component(express-server)
---
apiVersion: apps/v1
kind: Deployment
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: WORKLOAD
workload.oam.dev/type: webservice
name: express-server
namespace: default
spec:
replicas: 1
selector:
matchLabels:
app.oam.dev/component: express-server
template:
metadata:
labels:
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
spec:
containers:
- image: oamdev/hello-world
name: express-server
ports:
- containerPort: 8000
name: port-8000
protocol: TCP
---
## From the auxiliary workload
apiVersion: v1
kind: Service
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: TRAIT
trait.oam.dev/resource: webserviceExpose
trait.oam.dev/type: AuxiliaryWorkload
name: express-server
namespace: default
spec:
ports:
- name: port-8000
port: 8000
targetPort: 8000
selector:
app.oam.dev/component: express-server
type: ClusterIP
---
---
# Application(first-vela-app with topology target-prod) -- Component(express-server)
---
apiVersion: apps/v1
kind: Deployment
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: WORKLOAD
workload.oam.dev/type: webservice
name: express-server
namespace: default
spec:
replicas: 5
selector:
matchLabels:
app.oam.dev/component: express-server
template:
metadata:
labels:
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
spec:
containers:
- image: oamdev/hello-world
name: express-server
ports:
- containerPort: 8000
name: port-8000
protocol: TCP
---
## From the auxiliary workload
apiVersion: v1
kind: Service
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: TRAIT
trait.oam.dev/resource: webserviceExpose
trait.oam.dev/type: AuxiliaryWorkload
name: express-server
namespace: default
spec:
ports:
- name: port-8000
port: 8000
targetPort: 8000
selector:
app.oam.dev/component: express-server
type: ClusterIP
---
```
Each deploy workflow step with topology policy will render individual result.
It can be a bit redundant for you as you may just need to dry run for one environment at a time. The, you can use the external workflow feature like below.
Firstly, define policy and workflow as below in individual files:
* The `target-prod.yaml` and `ha.yaml` corresponding to the `production` environment.
```yaml
# target-prod.yaml
apiVersion: core.oam.dev/v1alpha1
kind: Policy
metadata:
name: target-prod
type: topology
properties:
clusters: ["local"]
namespace: "prod"
```
```yaml
# ha.yaml
apiVersion: core.oam.dev/v1alpha1
kind: Policy
metadata:
name: ha
type: override
properties:
components:
- type: webservice
traits:
- type: scaler
properties:
replicas: 5
```
* The `prod-workflow.yaml` can glue them together.
```yaml
# prod-workflow.yaml
apiVersion: core.oam.dev/v1alpha1
kind: Workflow
metadata:
name: deploy-prod
steps:
- type: deploy
name: deploy-prod
properties:
policies: ["ha", "target-prod"]
```
* Then the application can reference the workflow as below.
```yaml
apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: first-vela-app
spec:
components:
- name: express-server
type: webservice
properties:
image: oamdev/hello-world
ports:
- port: 8000
expose: true
traits:
- type: scaler
properties:
replicas: 1
workflow:
ref: deploy-prod
```
The dry run command can be:
```
vela dry-run -f app.yaml -f target-prod.yaml -f ha.yaml -f prod-workflow.yaml
```
Then, the dry-run results will only contain resources in the `production` environment.
expected output
```yaml
---
# Application(first-vela-app with topology target-prod) -- Component(express-server)
---
apiVersion: apps/v1
kind: Deployment
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: WORKLOAD
workload.oam.dev/type: webservice
name: express-server
namespace: default
spec:
replicas: 5
selector:
matchLabels:
app.oam.dev/component: express-server
template:
metadata:
labels:
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
spec:
containers:
- image: oamdev/hello-world
name: express-server
ports:
- containerPort: 8000
name: port-8000
protocol: TCP
---
## From the auxiliary workload
apiVersion: v1
kind: Service
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: TRAIT
trait.oam.dev/resource: webserviceExpose
trait.oam.dev/type: AuxiliaryWorkload
name: express-server
namespace: default
spec:
ports:
- name: port-8000
port: 8000
targetPort: 8000
selector:
app.oam.dev/component: express-server
type: ClusterIP
---
```
Moreover, you can use `--merge` flag to merge external policies and workflow when application file is not reference to them.
For example, you can define the application as below, the only difference is there's no `workflow` field.
```yaml
# app.yaml
apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
name: first-vela-app
spec:
components:
- name: express-server
type: webservice
properties:
image: oamdev/hello-world
ports:
- port: 8000
expose: true
traits:
- type: scaler
properties:
replicas: 1
```
the workflow and policy can be defined the same way
```yaml
# workflow.yaml
apiVersion: core.oam.dev/v1alpha1
kind: Workflow
metadata:
name: deploy-demo
steps:
- type: deploy
name: deploy-prod
properties:
policies: ["target-prod"]
```
```yaml
# target-prod.yaml
apiVersion: core.oam.dev/v1alpha1
kind: Policy
metadata:
name: target-prod
type: topology
properties:
clusters: ["local"]
namespace: "prod"
```
If you don't use `--merge` flag in this way, it will report warnings as below.
```
vela dry-run -f app.yaml -f target-prod.yaml -f workflow.yaml
```
result with warning messages
```yaml
WARNING: workflow deploy-demo not referenced by application
WARNING: policy target-prod not referenced by application
---
# Application(default) -- Component(express-server)
---
apiVersion: apps/v1
kind: Deployment
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: WORKLOAD
workload.oam.dev/type: webservice
name: express-server
namespace: default
spec:
replicas: 1
selector:
matchLabels:
app.oam.dev/component: express-server
template:
metadata:
labels:
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
spec:
containers:
- image: oamdev/hello-world
name: express-server
ports:
- containerPort: 8000
name: port-8000
protocol: TCP
---
## From the auxiliary workload
apiVersion: v1
kind: Service
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: TRAIT
trait.oam.dev/resource: webserviceExpose
trait.oam.dev/type: AuxiliaryWorkload
name: express-server
namespace: default
spec:
ports:
- name: port-8000
port: 8000
targetPort: 8000
selector:
app.oam.dev/component: express-server
type: ClusterIP
---
```
In this case, the policy and workflow do not take effect. Because those are not referenced by the application and being viewed as standalone files and ignored.
So to make those external files work, please provide "--merge" flag as below:
```
vela dry-run -f app.yaml -f target-prod.yaml -f workflow.yaml --merge
```
Then the application will be glued with external policies and workflows even no reference exists.
expected ouput
```yaml
---
# Application(first-vela-app with topology target-prod) -- Component(express-server)
---
apiVersion: apps/v1
kind: Deployment
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: WORKLOAD
workload.oam.dev/type: webservice
name: express-server
namespace: default
spec:
replicas: 1
selector:
matchLabels:
app.oam.dev/component: express-server
template:
metadata:
labels:
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
spec:
containers:
- image: oamdev/hello-world
name: express-server
ports:
- containerPort: 8000
name: port-8000
protocol: TCP
---
## From the auxiliary workload
apiVersion: v1
kind: Service
metadata:
annotations: {}
labels:
app.oam.dev/appRevision: ""
app.oam.dev/component: express-server
app.oam.dev/name: first-vela-app
app.oam.dev/namespace: default
app.oam.dev/resourceType: TRAIT
trait.oam.dev/resource: webserviceExpose
trait.oam.dev/type: AuxiliaryWorkload
name: express-server
namespace: default
spec:
ports:
- name: port-8000
port: 8000
targetPort: 8000
selector:
app.oam.dev/component: express-server
type: ClusterIP
---
```
You can refer to the [Dry run command](../cli/vela_dry-run.md) for more command line use cases.
## Dry run via UI
Clicking the `Deploy` button to open the workflow selector dialog. You could select a workflow(every workflow corresponding to an environment) and click the `DryRun` button to execute a dry run. If passed, the result is like this
The result report is different from the CLI, there is a complete application configuration that is generated from the application metadata, you could check it. Different environments may have different application configurations.