kubectl logs returns nothing (blank) - kubernetes

Question

kubectl logs web-deployment-76789f7f64-s2b4r
returns nothing! The console prompt returns without error.
I have a pod which is in a CrashLoopbackOff cycle (but am unable to diagnose it) -->
web-deployment-7f985968dc-rhx52 0/1 CrashLoopBackOff 6 7m
I am using Azure AKS with kubectl on Windows. I have been running this cluster for a few months without probs. The container runs fine on my workstation with docker-compose.
kubectl describe doesn't really help much - no useful information there.
kubectl describe pod web-deployment-76789f7f64-s2b4r
Name: web-deployment-76789f7f64-j6z5h
Namespace: default
Node: aks-nodepool1-35657602-0/10.240.0.4
Start Time: Thu, 10 Jan 2019 18:58:35 +0000
Labels: app=stweb
pod-template-hash=3234593920
Annotations: <none>
Status: Running
IP: 10.244.0.25
Controlled By: ReplicaSet/web-deployment-76789f7f64
Containers:
stweb:
Container ID: docker://d1e184a49931bd01804ace51cb44bb4e3479786ec0df6e406546bfb27ab84e31
Image: virasana/stwebapi:2.0.20190110.20
Image ID: docker-pullable://virasana/stwebapi#sha256:2a1405f30c358f1b2a2579c5f3cc19b7d3cc8e19e9e6dc0061bebb732a05d394
Port: 80/TCP
Host Port: 0/TCP
State: Waiting
Reason: CrashLoopBackOff
Last State: Terminated
Reason: Completed
Exit Code: 0
Started: Thu, 10 Jan 2019 18:59:27 +0000
Finished: Thu, 10 Jan 2019 18:59:27 +0000
Ready: False
Restart Count: 3
Environment:
SUPPORT_TICKET_DEPLOY_DB_CONN_STRING_AUTH: <set to the key 'SUPPORT_TICKET_DEPLOY_DB_CONN_STRING_AUTH' in secret 'mssql'> Optional: false
SUPPORT_TICKET_DEPLOY_DB_CONN_STRING: <set to the key 'SUPPORT_TICKET_DEPLOY_DB_CONN_STRING' in secret 'mssql'> Optional: false
SUPPORT_TICKET_DEPLOY_JWT_SECRET: <set to the key 'SUPPORT_TICKET_DEPLOY_JWT_SECRET' in secret 'mssql'> Optional: false
KUBERNETES_PORT_443_TCP_ADDR: kscluster-rgksk8s-2cfe9c-8af10e3f.hcp.eastus.azmk8s.io
KUBERNETES_PORT: tcp://kscluster-rgksk8s-2cfe9c-8af10e3f.hcp.eastus.azmk8s.io:443
KUBERNETES_PORT_443_TCP: tcp://kscluster-rgksk8s-2cfe9c-8af10e3f.hcp.eastus.azmk8s.io:443
KUBERNETES_SERVICE_HOST: kscluster-rgksk8s-2cfe9c-8af10e3f.hcp.eastus.azmk8s.io
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-98c7q (ro)
Conditions:
Type Status
Initialized True
Ready False
PodScheduled True
Volumes:
default-token-98c7q:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-98c7q
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
node.kubernetes.io/unreachable:NoExecute for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 1m default-scheduler Successfully assigned web-deployment-76789f7f64-j6z5h to aks-nodepool1-35657602-0
Normal SuccessfulMountVolume 1m kubelet, aks-nodepool1-35657602-0 MountVolume.SetUp succeeded for volume "default-token-98c7q"
Normal Pulled 24s (x4 over 1m) kubelet, aks-nodepool1-35657602-0 Container image "virasana/stwebapi:2.0.20190110.20" already present on machine
Normal Created 22s (x4 over 1m) kubelet, aks-nodepool1-35657602-0 Created container
Normal Started 22s (x4 over 1m) kubelet, aks-nodepool1-35657602-0 Started container
Warning BackOff 7s (x6 over 1m) kubelet, aks-nodepool1-35657602-0 Back-off restarting failed container
Any ideas on how to proceed?
Many Thanks!

Answer 1

I am using a multi-stage docker build, and was building using the wrong target! (I had cloned a previous Visual Studio docker build task, which had the following argument:
--target=test
Because the "test" build stage has no defined entry point, the container was launching and then exiting without logging anything! So that's why kubectl logs returned blank.
I changed this to
--target=final
and all is working!
My Dockerfile looks like this:
FROM microsoft/dotnet:2.1-aspnetcore-runtime AS base
WORKDIR /app
EXPOSE 80
FROM microsoft/dotnet:2.1-sdk AS build
WORKDIR /src
COPY . .
WORKDIR "/src"
RUN dotnet clean ./ST.Web/ST.Web.csproj
RUN dotnet build ./ST.Web/ST.Web.csproj -c Release -o /app
FROM build AS test
RUN dotnet tool install -g dotnet-reportgenerator-globaltool
RUN chmod 755 ./run-tests.sh && ./run-tests.sh
FROM build AS publish
RUN dotnet publish ./ST.Web/ST.Web.csproj -c Release -o /app
FROM base AS final
WORKDIR /app
COPY --from=publish /app .
ENTRYPOINT ["dotnet", "ST.Web.dll"]

Answer 2

that happens because pod is already destroyed, try doing:
kubectl logs web-deployment-76789f7f64-s2b4r --previous
this will show logs from the previous pod.

Answer 3

For me, I had published a wrong dll on my docker file. After correcting it, everything is working as expected.