The following narrative is based on the assumption that a Kubernetes (current stable version 20.10) has been setup using MetalLB Ingress controller. This should also work with Traefik or other load balancers.

# Create a separate namespace for this project
kubectl create namespace graylog

# Change into the graylog namespace
kubectl config set-context --current --namespace=graylog
kubectl config view --minify | grep namespace: # Validate it

# Optional: delete previous test instances of graylog that have been deployed via Helm
helm delete "graylog" --namespace graylog
kubectl delete pvc --namespace graylog --all

# How to switch execution context back to the 'default' namespace
kubectl config set-context --current --namespace=default

# Optional: installing mongdb prior to Graylog
helm install "mongodb" bitnami/mongodb --namespace "graylog" \
  --set persistence.size=100Gi
# Sample output:
NAME: mongodb
LAST DEPLOYED: Thu Aug 29 00:07:36 2021
NAMESPACE: graylog
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES:
** Please be patient while the chart is being deployed **
MongoDB® can be accessed on the following DNS name(s) and ports from within your cluster:
    mongodb.graylog.svc.cluster.local
To get the root password run:
    export MONGODB_ROOT_PASSWORD=$(kubectl get secret --namespace graylog mongodb -o jsonpath="{.data.mongodb-root-password}" | base64 --decode)
To connect to your database, create a MongoDB® client container:
    kubectl run --namespace graylog mongodb-client --rm --tty -i --restart='Never' --env="MONGODB_ROOT_PASSWORD=$MONGODB_ROOT_PASSWORD" --image docker.io/bitnami/mongodb:4.4.8-debian-10-r9 --command -- bash
Then, run the following command:
    mongo admin --host "mongodb" --authenticationDatabase admin -u root -p $MONGODB_ROOT_PASSWORD
To connect to your database from outside the cluster execute the following commands:
    kubectl port-forward --namespace graylog svc/mongodb 27017:27017 &
    mongo --host 127.0.0.1 --authenticationDatabase admin -p $MONGODB_ROOT_PASSWORD

# REQUIRED: Pre-install ElasticSearch version 7.10 as highest being supported by Graylog 4.1.3
# Source: https://artifacthub.io/packages/helm/elastic/elasticsearch/7.10.2
helm repo add elastic https://helm.elastic.co
helm repo update
helm install elasticsearch elastic/elasticsearch --namespace "graylog" \
  --set imageTag=7.10.2 \
  --set data.persistence.size=100Gi
# Sample output:
NAME: elasticsearch
LAST DEPLOYED: Sun Aug 29 04:35:30 2021
NAMESPACE: graylog
STATUS: deployed
REVISION: 1
NOTES:
1. Watch all cluster members come up.
  $ kubectl get pods --namespace=graylog -l app=elasticsearch-master -w
2. Test cluster health using Helm test.
  $ helm test elasticsearch

# Installation of Graylog with mongodb bundled, while integrating with a pre-deployed elasticSearch instance
#
# This install command assumes that the protocol preference for transporting logs is TCP
# Also, the current helm chart does not allow mixing TCP with UDP; therefore, this approach is conveniently
# matching business requirements where a reliable transmission TCP protocol is necessary to record security data.
helm install graylog kongz/graylog --namespace "graylog" \
  --set graylog.image.repository="graylog/graylog:4.1.3-1" \
  --set graylog.persistence.size=200Gi \
  --set graylog.service.type=LoadBalancer \
  --set graylog.service.port=80 \
  --set graylog.service.loadBalancerIP=10.10.100.88 \
  --set graylog.service.externalTrafficPolicy=Local \
  --set graylog.service.ports[0].name=gelf \
  --set graylog.service.ports[0].port=12201 \
  --set graylog.service.ports[1].name=syslog \
  --set graylog.service.ports[1].port=514 \
  --set graylog.rootPassword="SOMEPASSWORD" \
  --set tags.install-elasticsearch=false \
  --set graylog.elasticsearch.version=7 \
  --set graylog.elasticsearch.hosts=http://elasticsearch-master.graylog.svc.cluster.local:9200

# Optional: add these lines if the mongodb component has been installed separately
  --set tags.install-mongodb=false \
  --set graylog.mongodb.uri=mongodb://mongodb-mongodb-replicaset-0.mongodb-mongodb-replicaset.graylog.svc.cluster.local:27017/graylog?replicaSet=rs0 \

# Moreover, the graylog chart version 1.8.4 doesn't seem to set externalTrafficPolicy as expected.
# Set externalTrafficPolicy = local to preserve source client IPs
kubectl patch svc graylog-web -n graylog -p '{"spec":{"externalTrafficPolicy":"Local"}}'

# Sometimes, the static EXTERNAL-IP would be assigned to graylog-master, where graylog-web EXTERNAL-IP would
# remain in the status of <pending> indefinitely.
# Workaround: set services to share a single external IP
kubectl patch svc graylog-web -p '{"metadata":{"annotations":{"metallb.universe.tf/allow-shared-ip":"graylog"}}}'
kubectl patch svc graylog-master -p '{"metadata":{"annotations":{"metallb.universe.tf/allow-shared-ip":"graylog"}}}'
kubectl patch svc graylog-master -n graylog -p '{"spec": {"type": "LoadBalancer", "externalIPs":["10.10.100.88"]}}'
kubectl patch svc graylog-web -n graylog -p '{"spec": {"type": "LoadBalancer", "externalIPs":["10.10.100.88"]}}'

# Test sending logs to server via TCP
graylog-server=graylog.kimconnect.com
echo -e '{"version": "1.1","host":"kimconnect.com","short_message":"Short message","full_message":"This is a\n\nlong message","level":9000,"_user_id":9000,"_ip_address":"1.1.1.1","_location":"LAX"}\0' | nc -w 1 $graylog-server 514

# Test via UDP
graylog-server=graylog.kimconnect.com
echo -e '{"version": "1.1","host":"kimconnect.com","short_message":"Short message","full_message":"This is a\n\nlong message","level":9000,"_user_id":9000,"_ip_address":"1.1.1.1","_location":"LAX"}\0' | nc -u -w 1 $graylog-server 514

# Optional: graylog Ingress
cat > graylog-ingress.yaml <<EOF
kind: Ingress
apiVersion: networking.k8s.io/v1
metadata:
  name: graylog-ingress
  namespace: graylog
  annotations:
    kubernetes.io/ingress.class: "nginx"
    # set these for SSL
    # ingress.kubernetes.io/rewrite-target: /
    # acme http01
    # acme.cert-manager.io/http01-edit-in-place: "true"
    # acme.cert-manager.io/http01-ingress-class: "true"
    # kubernetes.io/tls-acme: "true"  
spec:
  rules:
  - host: graylog.kimconnect.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: graylog-web
            port:
              number: 80
      - path: /
        pathType: Prefix
        backend:
          service:
            name: graylog-web
            port:
              number: 12201
      - path: /
        pathType: Prefix
        backend:
          service:
            name: graylog-web
            port:
              number: 514              
EOF
kubectl apply -f graylog-ingress.yaml

Troubleshooting Notes:

# Sample commands to patch graylog service components
kubectl patch svc graylog-web -p '{"spec":{"type":"LoadBalancer"}}' # Convert ClusterIP to LoadBalancer to gain ingress
kubectl patch svc graylog-web -p '{"spec":{"externalIPs":["10.10.100.88"]}}' # Add externalIPs
kubectl patch svc graylog-master -n graylog -p '{"spec":{"loadBalancerIP":""}}' # Remove loadBalancer IPs
kubectl patch svc graylog-master -n graylog -p '{"status":{"loadBalancer":{"ingress":[]}}}' # Purge ingress IPs
kubectl patch svc graylog-web -n graylog -p '{"status":{"loadBalancer":{"ingress":[{"ip":"10.10.100.88"}]}}}'
kubectl patch svc graylog-web -n graylog -p '{"status":{"loadBalancer":{"ingress":[]}}}'

# Alternative solution: mixing UDP with TCP
# The current chart version only allows this when service Type = ClusterIP (default)
helm upgrade graylog kongz/graylog --namespace "graylog" \
  --set graylog.image.repository="graylog/graylog:4.1.3-1" \
  --set graylog.persistence.size=200Gi \
  --set graylog.service.externalTrafficPolicy=Local \
  --set graylog.service.port=80 \
  --set graylog.service.ports[0].name=gelf \
  --set graylog.service.ports[0].port=12201 \
  --set graylog.service.ports[0].protocol=UDP \
  --set graylog.service.ports[1].name=syslog \
  --set graylog.service.ports[1].port=514 \
  --set graylog.service.ports[1].protocol=UDP \
  --set graylog.rootPassword="SOMEPASSWORD" \
  --set tags.install-elasticsearch=false \
  --set graylog.elasticsearch.version=7 \
  --set graylog.elasticsearch.hosts=http://elasticsearch-master.graylog.svc.cluster.local:9200

# Error message occurs when combing TCP with UDP; hence, a ClusterIP must be specified
Error: UPGRADE FAILED: cannot patch "graylog-web" with kind Service: Service "graylog-web" is invalid: spec.ports: Invalid value: []core.ServicePort{core.ServicePort{Name:"graylog", Protocol:"TCP", AppProtocol:(*string)(nil), Port:80, TargetPort:intstr.IntOrString{Type:0, IntVal:9000, StrVal:""}, NodePort:32518}, core.ServicePort{Name:"gelf", Protocol:"UDP", AppProtocol:(*string)(nil), Port:12201, TargetPort:intstr.IntOrString{Type:0, IntVal:12201, StrVal:""}, NodePort:0}, core.ServicePort{Name:"gelf2", Protocol:"TCP", AppProtocol:(*string)(nil), Port:12222, TargetPort:intstr.IntOrString{Type:0, IntVal:12222, StrVal:""}, NodePort:31523}, core.ServicePort{Name:"syslog", Protocol:"TCP", AppProtocol:(*string)(nil), Port:514, TargetPort:intstr.IntOrString{Type:0, IntVal:514, StrVal:""}, NodePort:31626}}: may not contain more than 1 protocol when type is 'LoadBalancer'

# Set array type value instead of string
Error: UPGRADE FAILED: error validating "": error validating data: ValidationError(Service.spec.externalIPs): invalid type for io.k8s.api.core.v1.ServiceSpec.externalIPs: got "string", expected "array"
# Solution:
--set "array={a,b,c}" OR --set service[0].port=80

# Graylog would not start and this was the error:
com.github.joschi.jadconfig.ValidationException: Parent directory /usr/share/graylog/data/journal for Node ID file at /usr/share/graylog/data/journal/node-id is not writable

# Workaround
graylogData=/mnt/k8s/graylog-journal-graylog-0-pvc-04dd9c7f-a771-4041-b549-5b4664de7249/
chown -fR 1100:1100 $graylogData

NAME: graylog
LAST DEPLOYED: Thu Aug 29 03:26:00 2021
NAMESPACE: graylog
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES:
To connect to your Graylog server:
1. Get the application URL by running these commands:
  Graylog Web Interface uses JavaScript to get detail of each node. The client JavaScript cannot communicate to node when service type is `ClusterIP`.
  If you want to access Graylog Web Interface, you need to enable Ingress.
    NOTE: Port Forward does not work with web interface.
2. The Graylog root users
  echo "User: admin"
  echo "Password: $(kubectl get secret --namespace graylog graylog -o "jsonpath={.data['graylog-password-secret']}" | base64 --decode)"
To send logs to graylog:
  NOTE: If `graylog.input` is empty, you cannot send logs from other services. Please make sure the value is not empty.
        See https://github.com/KongZ/charts/tree/main/charts/graylog#input for detail

k describe pod graylog-0
Events:
  Type     Reason            Age                   From               Message
  ----     ------            ----                  ----               -------
  Warning  FailedScheduling  11m                   default-scheduler  0/4 nodes are available: 4 pod has unbound immediate PersistentVolumeClaims.
  Warning  FailedScheduling  11m                   default-scheduler  0/4 nodes are available: 4 pod has unbound immediate PersistentVolumeClaims.
  Normal   Scheduled         11m                   default-scheduler  Successfully assigned graylog/graylog-0 to linux03
  Normal   Pulled            11m                   kubelet            Container image "alpine" already present on machine
  Normal   Created           11m                   kubelet            Created container setup
  Normal   Started           10m                   kubelet            Started container setup
  Normal   Started           4m7s (x5 over 10m)    kubelet            Started container graylog-server
  Warning  Unhealthy         3m4s (x4 over 9m14s)  kubelet            Readiness probe failed: Get "http://172.16.90.197:9000/api/system/lbstatus": dial tcp 172.16.90.197:9000: connect: connection refused
  Normal   Pulled            2m29s (x6 over 10m)   kubelet            Container image "graylog/graylog:4.1.3-1" already present on machine
  Normal   Created           2m19s (x6 over 10m)   kubelet            Created container graylog-server
  Warning  BackOff           83s (x3 over 2m54s)   kubelet            Back-off restarting failed container

Readiness probe failed: Get http://api/system/lbstatus: dial tcp 172.16.90.197:9000: connect: connection refused

# Set external IP
# This only works on LoadBalancer, not ClusterIP
# kubectl patch svc graylog-web -p '{"spec":{"externalIPs":["10.10.100.88"]}}'
# kubectl patch svc graylog-master -p '{"spec":{"externalIPs":[]}}'

kubectl patch service graylog-web --type='json' -p='[{"op": "add", "path": "/metadata/annotations/kubernetes.io~1ingress.class", "value":"nginx"}]'

# Set annotation to allow shared IPs between 2 different services
kubectl annotate service graylog-web metallb.universe.tf/allow-shared-ip=graylog
kubectl annotate service graylog-master metallb.universe.tf/allow-shared-ip=graylog

metadata:
  name: $serviceName-tcp
  annotations:
    metallb.universe.tf/address-pool: default
    metallb.universe.tf/allow-shared-ip: psk

# Ingress
appName=graylog
domain=graylog.kimconnect.com
deploymentName=graylog-web
containerPort=9000
cat <<EOF> $appName-ingress.yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: $appName-ingress
  annotations:
    kubernetes.io/ingress.class: "nginx"
    # ingress.kubernetes.io/rewrite-target: /
    # acme http01
    # acme.cert-manager.io/http01-edit-in-place: "true"
    # acme.cert-manager.io/http01-ingress-class: "true"
    # kubernetes.io/tls-acme: "true"
spec:
  rules:
  - host: $domain
    http:
      paths:
      - backend:
          service:
            name: $deploymentName
            port:
              number: 9000
        path: /
        pathType: Prefix
EOF
kubectl apply -f $appName-ingress.yaml

# delete pvc's
namespace=graylog
kubectl delete pvc data-graylog-elasticsearch-data-0 -n $namespace
kubectl delete pvc data-graylog-elasticsearch-master-0 -n $namespace
kubectl delete pvc datadir-graylog-mongodb-0 -n $namespace
kubectl delete pvc journal-graylog-0 -n $namespace

# delete all pvc's in namespace the easier way
namespace=graylog
kubectl get pvc -n $namespace | awk '$1 {print$1}' | while read vol; do kubectl delete pvc/${vol} -n $namespace; done

2021-08-20 20:19:41,048 INFO    [cluster] - Exception in monitor thread while connecting to server mongodb-mongodb-replicaset-0.mongodb-mongodb-replicaset.graylog.svc.cluster.local:27017 - {}
com.mongodb.MongoSocketException: mongodb-mongodb-replicaset-0.mongodb-mongodb-replicaset.graylog.svc.cluster.local
        at com.mongodb.ServerAddress.getSocketAddresses(ServerAddress.java:211) ~[graylog.jar:?]
        at com.mongodb.internal.connection.SocketStream.initializeSocket(SocketStream.java:75) ~[graylog.jar:?]
        at com.mongodb.internal.connection.SocketStream.open(SocketStream.java:65) ~[graylog.jar:?]
        at com.mongodb.internal.connection.InternalStreamConnection.open(InternalStreamConnection.java:128) ~[graylog.jar:?]
        at com.mongodb.internal.connection.DefaultServerMonitor$ServerMonitorRunnable.run(DefaultServerMonitor.java:117) [graylog.jar:?]
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_302]
Caused by: java.net.UnknownHostException: mongodb-mongodb-replicaset-0.mongodb-mongodb-replicaset.graylog.svc.cluster.local
        at java.net.InetAddress.getAllByName0(InetAddress.java:1281) ~[?:1.8.0_302]
        at java.net.InetAddress.getAllByName(InetAddress.java:1193) ~[?:1.8.0_302]
        at java.net.InetAddress.getAllByName(InetAddress.java:1127) ~[?:1.8.0_302]
        at com.mongodb.ServerAddress.getSocketAddresses(ServerAddress.java:203) ~[graylog.jar:?]
        ... 5 more

2021-08-20 20:19:42,981 INFO    [cluster] - No server chosen by com.mongodb.client.internal.MongoClientDelegate$1@69419d59 from cluster description ClusterDescription{type=REPLICA_SET, connectionMode=MULTIPLE, serverDescriptions=[ServerDescription{address=mongodb-mongodb-replicaset-0.mongodb-mongodb-replicaset.graylog.svc.cluster.local:27017, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketException: mongodb-mongodb-replicaset-0.mongodb-mongodb-replicaset.graylog.svc.cluster.local}, caused by {java.net.UnknownHostException: mongodb-mongodb-replicaset-0.mongodb-mongodb-replicaset.graylog.svc.cluster.local}}]}. Waiting for 30000 ms before timing out - {}

# Alternative version - that doesn't work
# helm repo add groundhog2k https://groundhog2k.github.io/helm-charts/
# helm install graylog groundhog2k/graylog --namespace "graylog" \
#   --set image.tag=4.1.3-1 \
#   --set settings.http.publishUri='http://127.0.0.1:9000/' \
#   --set service.type=LoadBalancer \
#   --set service.loadBalancerIP=192.168.100.88 \
#   --set elasticsearch.enabled=true \
#   --set mongodb.enabled=true

# helm upgrade graylog groundhog2k/graylog --namespace "graylog" \
#   --set image.tag=4.1.3-1 \
#   --set settings.http.publishUri=http://localhost:9000/ \
#   --set service.externalTrafficPolicy=Local \
#   --set service.type=LoadBalancer \
#   --set service.loadBalancerIP=192.168.100.88 \
#   --set elasticsearch.enabled=true \
#   --set mongodb.enabled=true \
#   --set storage.className=nfs-client \
#   --set storage.requestedSize=200Gi

# kim@linux01:~$ k logs graylog-0
# 2021-08-29 03:47:09,345 ERROR: org.graylog2.bootstrap.CmdLineTool - Invalid configuration
# com.github.joschi.jadconfig.ValidationException: Couldn't run validator method
#         at com.github.joschi.jadconfig.JadConfig.invokeValidatorMethods(JadConfig.java:227) ~[graylog.jar:?]
#         at com.github.joschi.jadconfig.JadConfig.process(JadConfig.java:100) ~[graylog.jar:?]
#         at org.graylog2.bootstrap.CmdLineTool.processConfiguration(CmdLineTool.java:420) [graylog.jar:?]
#         at org.graylog2.bootstrap.CmdLineTool.run(CmdLineTool.java:236) [graylog.jar:?]
#         at org.graylog2.bootstrap.Main.main(Main.java:45) [graylog.jar:?]
# Caused by: java.lang.reflect.InvocationTargetException
#         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_302]
#         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_302]
#         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_302]
#         at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_302]
#         at com.github.joschi.jadconfig.ReflectionUtils.invokeMethodsWithAnnotation(ReflectionUtils.java:53) ~[graylog.jar:?]
#         at com.github.joschi.jadconfig.JadConfig.invokeValidatorMethods(JadConfig.java:221) ~[graylog.jar:?]
#         ... 4 more
# Caused by: java.lang.IllegalArgumentException: URLDecoder: Illegal hex characters in escape (%) pattern - For input string: "!s"
#         at java.net.URLDecoder.decode(URLDecoder.java:194) ~[?:1.8.0_302]
#         at com.mongodb.ConnectionString.urldecode(ConnectionString.java:1035) ~[graylog.jar:?]
#         at com.mongodb.ConnectionString.urldecode(ConnectionString.java:1030) ~[graylog.jar:?]
#         at com.mongodb.ConnectionString.<init>(ConnectionString.java:336) ~[graylog.jar:?]
#         at com.mongodb.MongoClientURI.<init>(MongoClientURI.java:256) ~[graylog.jar:?]
#         at org.graylog2.configuration.MongoDbConfiguration.getMongoClientURI(MongoDbConfiguration.java:59) ~[graylog.jar:?]
#         at org.graylog2.configuration.MongoDbConfiguration.validate(MongoDbConfiguration.java:64) ~[graylog.jar:?]
#         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_302]
#         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_302]
#         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_302]
#         at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_302]
#         at com.github.joschi.jadconfig.ReflectionUtils.invokeMethodsWithAnnotation(ReflectionUtils.java:53) ~[graylog.jar:?]
#         at com.github.joschi.jadconfig.JadConfig.invokeValidatorMethods(JadConfig.java:221) ~[graylog.jar:?]