Why my canary deployment does not work with istio? - docker

Question

I am trying to learn the basics about istio so I have gone through the official documentation here in order to create a 80/20 canary deployment, I have also follow this guide from digitalocean which explains it very easy for a simple deployment https://www.digitalocean.com/community/tutorials/how-to-do-canary-deployments-with-istio-and-kubernetes.
I have created a simple app with 2 different messages on the homepage, and then created the virtualService, Gateway and the destination rules. I (as mentioned in the guide) get the external ip with kubectl -n istio-system get svc and the try to navigate to that address but I get a 503 error. It seems very simple but I have to be missing something. These are my 3 files (as far as I understand there are no more necessary files):
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
namespace: istio
name: flask-gateway
spec:
selector:
istio: ingressgateway
servers:
- hosts:
- "*"
port:
name: http
number: 80
protocol: HTTP
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
name: flask-app
namespace: istio
spec:
hosts:
- "*"
gateways:
- flask-gateway
http:
- route:
- destination:
host: flask-app
subset: v1
weight: 80
- destination:
host: flask-app
subset: v2
weight: 20
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
name: flask-app
namespace: istio
spec:
host: flask-app
subsets:
- name: v1
labels:
version: v1
- name: v2
labels:
version: v2
Here are the yaml with deployment and services for v1 and v2:
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
version: v1
name: flask-deployment-v1
namespace: istio
spec:
replicas: 1
selector:
matchLabels:
app: flask-app
template:
metadata:
labels:
version: v1
app: flask-app
spec:
containers:
- name: flask-app
image: latalavera/flask-app:1.3
ports:
- containerPort: 5000
resources:
requests:
cpu: 100m
memory: 128Mi
limits:
cpu: 250m
memory: 256Mi
---
apiVersion: v1
kind: Service
metadata:
name: flask-service
namespace: istio
spec:
selector:
app: flask-app
ports:
- port: 5000
protocol: TCP
targetPort: 5000
type: ClusterIP
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
version: v2
name: flask-deployment-v2
namespace: istio
spec:
replicas: 1
selector:
matchLabels:
app: flask-app
template:
metadata:
labels:
app: flask-app
version: v2
spec:
containers:
- name: flask-app
image: latalavera/flask-app:2.0
ports:
- containerPort: 5000
resources:
requests:
cpu: 100m
memory: 128Mi
limits:
cpu: 250m
memory: 256Mi
---
apiVersion: v1
kind: Service
metadata:
name: flask-service2
namespace: istio
spec:
selector:
app: flask-app
ports:
- port: 5000
protocol: TCP
targetPort: 5000
type: ClusterIP
I have added the labels version: v1 and version: v2 to my deployments, and I have also used the kubectl label ns istio istio-injection=enabled command, but they are not working anyways

Answer 1

You named the service flask-service and set the host in your VirtualService to flask-app.
The host field is not a selector but the FQDN of the service you want to route the traffic to. So it should be called flask-service or better flask-service.istio.svc.cluster.local:
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
name: flask-app
namespace: istio
spec:
hosts:
- "*"
gateways:
- flask-gateway
http:
- route:
- destination:
host: flask-service.istio.svc.cluster.local
subset: v1
weight: 80
- destination:
host: flask-service.istio.svc.cluster.local
subset: v2
weight: 20
Alternatively you could just call the service flask-app like the Deployment. But using the full FQDN <service-name>.<namespace-name>.svc.cluster.local is recommended in any case. From docs:
Note for Kubernetes users: When short names are used (e.g. “reviews” instead of “reviews.default.svc.cluster.local”), Istio will interpret the short name based on the namespace of the rule, not the service. A rule in the “default” namespace containing a host “reviews” will be interpreted as “reviews.default.svc.cluster.local”, irrespective of the actual namespace associated with the reviews service. To avoid potential misconfigurations, it is recommended to always use fully qualified domain names over short names.
https://istio.io/latest/docs/reference/config/networking/virtual-service/#VirtualService -> hosts
You btw don't need 2 services, just one. Your service has a selector for app: flask-app so it can route traffic to v1 and v2. How the traffic is routed is defined by the VirtualService and DestionationRule. I would recommand to remove service flask-service2. If you need to route the traffic inside the mesh, add mesh as gateways in the VirtualService or create a new one for mesh internal traffic, to reach both versions. More on that topic:
https://istio.io/latest/docs/reference/config/networking/virtual-service/#VirtualService -> gateways