istio-pilot deployment fails when there is no LoadBalancer in the cluster

Context

Trying to run this test for kubeflow-tensorboards-operator (which is a simple "deploy and relate the minimum required charms" test), we noticed that istio-pilot charm would fail in different parts of its execution. The error always looked like the one below, but the hook failing could also be install, istio-pilot-relation-changed.

...
  File "./src/charm.py", line 827, in _get_address_from_loadbalancer
    if len(ingresses) != 1:
TypeError: object of type 'NoneType' has no len()
unit-istio-pilot-0: 15:19:55 ERROR juju.worker.uniter.operation hook "config-changed" (via hook dispatching script: dispatch) failed: exit status 1

Reproduce

Install and setup Microk8s

sudo snap install microk8s --classic --channel=1.24/stable
sudo usermod -a -G microk8s $USER
sudo chown -f -R $USER ~/.kube
microk8s status --wait-ready
microk8s.enable hostpath-storage dns 
sudo snap install juju --classic
juju bootstrap microk8s micro

git clone git@github.com:canonical/kubeflow-tensorboards-operator.git and cd kubeflow-tensorboards-operator
Install test requirements python3 -m pip install -r requirements-integration.txt
Run test with tox -e integration

Cause

It turns out the Microk8s cluster didn't have a LoadBalancer and Istio relies heavily on the underlying LB to configure the gateway (ingressgateway). Otherwise, the gateway will be waiting for an external IP and istio-pilot will fail due to the following lines where it checks the ingresses object's length before verifying that it is not None. Probably though, this is a case that the istio-pilot charm should be able to handle.

P.S. The error was gone as soon as I added a LB with microk8s enable metallb:10.64.140.43-10.64.140.49

I hit the same issue, and I'm using metallb configured like this:

IPADDR=$(ip -4 -j route get 2.2.2.2 | jq -r '.[] | .prefsrc') 
microk8s enable metallb:$IPADDR-$IPADDR

My environment:

$ microk8s version  
MicroK8s v1.28.10 revision 6829  
$ microk8s status                                                                                                                      
microk8s is running                                                                                                                          
high-availability: no                                                                                                                        
  datastore master nodes: 127.0.0.1:19001                                                                                                    
  datastore standby nodes: none                                                                                                              
addons:                                                                                                                                      
  enabled:                                                                                                                                   
    community            # (core) The community addons repository                                                                                                                                                                                                                         
    dashboard            # (core) The Kubernetes dashboard                                                                                   
    dns                  # (core) CoreDNS                                                                                                    
    ha-cluster           # (core) Configure high availability on the current node                                                            
    helm                 # (core) Helm - the package manager for Kubernetes                                                                  
    helm3                # (core) Helm 3 - the package manager for Kubernetes                                                                
    hostpath-storage     # (core) Storage class; allocates storage from host directory                                                       
    metallb              # (core) Loadbalancer for your Kubernetes cluster                                                                   
    metrics-server       # (core) K8s Metrics Server for API access to service metrics                                                       
    registry             # (core) Private image registry exposed on localhost:32000                                                          
    storage              # (core) Alias to hostpath-storage add-on, deprecated                                                               
  disabled:                                                                                                                                  
    argocd               # (community) Argo CD is a declarative continuous deployment for Kubernetes.                                        
    dashboard-ingress    # (community) Ingress definition for Kubernetes dashboard                                                           
    easyhaproxy          # (community) EasyHAProxy can configure HAProxy automatically based on ingress labels                               
    fluentd              # (community) Elasticsearch-Fluentd-Kibana logging and monitoring                                                   
    gopaddle             # (community) DevSecOps and Multi-Cloud Kubernetes Platform                                                         
    inaccel              # (community) Simplifying FPGA management in Kubernetes                                                             
    istio                # (community) Core Istio service mesh services                                                                                                                                                                                                                   
    jaeger               # (community) Kubernetes Jaeger operator with its simple config                                                                                                                                                                                                  
    keda                 # (community) Kubernetes-based Event Driven Autoscaling                                                                                                                                                                                                          
    knative              # (community) Knative Serverless and Event Driven Applications                                                                                                                                                                                                   
    linkerd              # (community) Linkerd is a service mesh for Kubernetes and other frameworks                                                                                                                                                                                      
    microcks             # (community) Open source Kubernetes Native tool for API Mocking and Testing                                                                                                                                                                                     
    openebs              # (community) OpenEBS is the open-source storage solution for Kubernetes                                                                                                                                                                                         
    openfaas             # (community) OpenFaaS serverless framework                                                                                                                                                                                                                      
    osm-edge             # (community) osm-edge is a lightweight SMI compatible service mesh for the edge-computing.                                                                                                                                                                      
    parking              # (community) Static webserver to park a domain. Works with EasyHAProxy.                                                                                                                                                                                         
    portainer            # (community) Portainer UI for your Kubernetes cluster                                                                                                                                                                                                           
    shifu                # (community) Kubernetes native IoT software development framework.                                                                                                                                                                                              
    sosivio              # (community) Kubernetes Predictive Troubleshooting, Observability, and Resource Optimization                                                                                                                                                                    
    traefik              # (community) traefik Ingress controller                                                                                                                                                                                                                         
    trivy                # (community) Kubernetes-native security scanner                                                                                                                                                                                                                 
    cert-manager         # (core) Cloud native certificate management                                                                                                                                                                                                                     
    cis-hardening        # (core) Apply CIS K8s hardening                                                                                                                                                                                                                                 
    host-access          # (core) Allow Pods connecting to Host services smoothly                                                                                                                                                                                                         
    ingress              # (core) Ingress controller for external access                                                                                                                                                                                                                  
    mayastor             # (core) OpenEBS MayaStor                                                                                                                                                                                                                                        
    minio                # (core) MinIO object storage                                                                                                                                                                                                                                    
    observability        # (core) A lightweight observability stack for logs, traces and metrics                                                                                                                                                                                          
    prometheus           # (core) Prometheus operator for monitoring and logging                                                                                                                                                                                                          
    rbac                 # (core) Role-Based Access Control for authorisation                                                                                                                                                                                                             
    rook-ceph            # (core) Distributed Ceph storage using Rook

canonical / istio-operators