Welcome to the Ingress Nginx new contributor tips. This guide briefly outlines the necessary knowledge & tools, required to start working on Ingress-NGINX Issues.
- Basic understanding of linux
- Familiarity with the command line on linux
- OSI Model(Links below)
It all starts with the OSI model...
The Open Systems Interconnection (OSI) model describes seven layers that computer systems use to communicate over a network. It was the first standard model for network communications, adopted by all major computer and telecommunication companies
Not everybody knows everything. But the factors that help are a love/passion for this to begin. But to move forward, its the approach and not the knowledge that sustains prolonged joy, while working on issues. If the approach is simple and powered by good-wishes-for-community, then info & tools are forthcoming and easy.
Here we take a bird's eye-view of the hops in the network plumbing, that a packet takes, from source to destination, when we run curl, from a laptop to a nginx webserver process, running in a container, inside a pod, inside a Kubernetes cluster, created using kind or minikube or any other cluster-management tool.
Kind cluster example on a Linux Host
The destination of the packet from the curl command, is looked up, in the routing table. Based on the route, the the packet first travels to the virtual bridge 172.18.0.1 interface, created by docker, when we created the kind cluster on a laptop. Next the packet is forwarded to 172.18.0.2(See below on how we got this IP address), within the kind cluster. The kube-proxy container creates iptables rules that make sure the packet goes to the correct pod ip in this case 10.244.0.5
Command:
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
230e7246a32c kindest/node:v1.24.1 "/usr/local/bin/entr…" 2 weeks ago Up 54 seconds 127.0.0.1:38143->6443/tcp kind-control-plane
# docker inspect kind-control-plane -f '{{ .NetworkSettings.Networks.kind.IPAddress }}'
172.18.0.2
If this part is confusing, you would first need to understand what a bridge is and what docker network is.
Let's begin with creating a Kind Cluster on your laptop
# kind create cluster
This will create a cluster called kind, to view the clusters type
# kind get clusters
kind
Kind ships with kubectl, so we can use that to communicate with our clusters.
# kubectl get no -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
kind-control-plane Ready control-plane 5d23h v1.24.1 172.18.0.2 <none> Ubuntu 21.10 5.18.12-arch1-1 containerd://1.6.4
Kind creates a cluster using docker container as nodes, it does this using containerd within the docker container. The concept of Docker in Docker is very important here.
To start with simply create a nginx deployment using kubectl.
# kubectl create deployment nginx --image nginx:alpine --port=80
deployment.apps/nginx created
Then we expose this as a NodePort Service.
# kubectl expose deployment/nginx --type=NodePort
service/nginx-new exposed
Command: Now we can see that the service has been exposed.
# kubectl get svc -o wide
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
nginx NodePort 10.96.176.241 <none> 80:32329/TCP 4d8h app=nginx
Output Relevance: From the above output, we can see that our nginx pod is being exposed as the NodePort service type, and now we can curl the Node IP 172.18.0.2 with the exposed port 32329
Command: The pod has an IP as shown below
# kubectl get po -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-6c8b449b8f-pdvdk 1/1 Running 1 (32h ago) 4d8h 10.244.0.5 kind-control-plane <none> <none>
Command: We can use curl on the laptop to view the nginx container that is running on port 32329.
# curl 172.18.0.2:32329
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
Now, we can check the ip interfaces as well subnets for our system is connected to:
$ ifconfig
ethbr0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.31.9 netmask 255.255.255.0 broadcast 192.168.31.255
inet6 fe80::7530:9ae5:3e8d:e45a prefixlen 64 scopeid 0x20<link>
ether 2e:90:b3:e8:52:5b txqueuelen 1000 (Ethernet)
RX packets 31220566 bytes 44930589084 (41.8 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 18104006 bytes 1757183680 (1.6 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
br-2fffe5cd5d9e: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.18.0.1 netmask 255.255.0.0 broadcast 172.18.255.255
inet6 fc00:f853:ccd:e793::1 prefixlen 64 scopeid 0x0<global>
inet6 fe80::42:12ff:fed3:8fb0 prefixlen 64 scopeid 0x20<link>
inet6 fe80::1 prefixlen 64 scopeid 0x20<link>
ether 02:42:12:d3:8f:b0 txqueuelen 0 (Ethernet)
RX packets 3547 bytes 414792 (405.0 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 6267 bytes 8189931 (7.8 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
docker0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
inet6 fe80::42:a2ff:fe09:5edb prefixlen 64 scopeid 0x20<link>
ether 02:42:a2:09:5e:db txqueuelen 0 (Ethernet)
RX packets 14 bytes 2143 (2.0 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 40 bytes 6406 (6.2 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
From the above output we can see that, there are two bridges connected to our systems network interface,one is the docker default bridgedocker0 and the other created by kind
br-2fffe5cd5d9e.
Since kind creates nodes as containers, this is easily accessible via docker ps.
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
230e7246a32c kindest/node:v1.24.1 "/usr/local/bin/entr…" 6 days ago Up 33 hours 127.0.0.1:38143->6443/tcp kind-control-plane
If we do a docker exec we can enter the container, we can also see the network interfaces within the container.
# docker exec -it 230e7246a32c bash
# root@kind-control-plane:/# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: vethdb0d1da1@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether a2:a1:ce:08:d2:39 brd ff:ff:ff:ff:ff:ff link-netns cni-ddc25710-030a-cc05-c600-5a183fae01f7
inet 10.244.0.1/32 scope global vethdb0d1da1
valid_lft forever preferred_lft forever
3: veth4d76603f@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 9a:9b:6b:3e:d1:53 brd ff:ff:ff:ff:ff:ff link-netns cni-f2270000-8fc8-6f89-e56b-4759ae10a084
inet 10.244.0.1/32 scope global veth4d76603f
valid_lft forever preferred_lft forever
4: vethcc2586d6@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 52:f9:20:63:62:a2 brd ff:ff:ff:ff:ff:ff link-netns cni-97e337cd-1322-c1fa-7523-789af94f397f
inet 10.244.0.1/32 scope global vethcc2586d6
valid_lft forever preferred_lft forever
5: veth783189a9@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether ba:e1:55:1f:6f:12 brd ff:ff:ff:ff:ff:ff link-netns cni-90849001-668a-03d2-7d9e-192de79ccc59
inet 10.244.0.1/32 scope global veth783189a9
valid_lft forever preferred_lft forever
6: veth79c98c12@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 22:05:55:c7:86:e9 brd ff:ff:ff:ff:ff:ff link-netns cni-734dfac9-9f70-ab33-265b-21569d90312a
inet 10.244.0.1/32 scope global veth79c98c12
valid_lft forever preferred_lft forever
7: veth5b221c83@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 92:3f:04:54:72:5a brd ff:ff:ff:ff:ff:ff link-netns cni-d8f6666b-1cfb-ef08-4bf8-237a7fc32da2
inet 10.244.0.1/32 scope global veth5b221c83
valid_lft forever preferred_lft forever
8: vethad630fb8@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 32:78:ec:f6:01:ea brd ff:ff:ff:ff:ff:ff link-netns cni-6cb3c179-cb17-3b81-2051-27231c44a3c4
inet 10.244.0.1/32 scope global vethad630fb8
valid_lft forever preferred_lft forever
9: veth573a629b@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether e2:57:f8:c9:bc:94 brd ff:ff:ff:ff:ff:ff link-netns cni-d2dbb903-8310-57b4-7ba4-9f353dbc79dc
inet 10.244.0.1/32 scope global veth573a629b
valid_lft forever preferred_lft forever
10: eth0@if11: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 02:42:ac:12:00:02 brd ff:ff:ff:ff:ff:ff link-netnsid 0
inet 172.18.0.2/16 brd 172.18.255.255 scope global eth0
valid_lft forever preferred_lft forever
inet6 fc00:f853:ccd:e793::2/64 scope global nodad
valid_lft forever preferred_lft forever
inet6 fe80::42:acff:fe12:2/64 scope link
valid_lft forever preferred_lft forever
11: vethd7368e27@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 8a:74:ec:f6:d6:c9 brd ff:ff:ff:ff:ff:ff link-netns cni-7c7eb9cd-bbb1-65b0-0480-b8f1265f2f36
inet 10.244.0.1/32 scope global vethd7368e27
valid_lft forever preferred_lft forever
12: veth7cadbf2b@if2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 12:48:10:b7:b8:f5 brd ff:ff:ff:ff:ff:ff link-netns cni-b39e37b5-1bc8-626a-a553-a0be2f94a117
inet 10.244.0.1/32 scope global veth7cadbf2b
valid_lft forever preferred_lft forever
When we run curl 172.18.0.2:32329 on the laptop it first needs to figure out where 172.18.0.2, to do this it refers to the host routing table.
sudo netstat -rn main
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 192.168.31.1 0.0.0.0 UG 0 0 0 ethbr0
172.17.0.0 0.0.0.0 255.255.0.0 U 0 0 0 docker0
172.18.0.0 0.0.0.0 255.255.0.0 U 0 0 0 br-2fffe5cd5d9e
172.19.0.0 0.0.0.0 255.255.0.0 U 0 0 0 br-be5b544733a3
192.168.31.0 0.0.0.0 255.255.255.0 U 0 0 0 ethbr0
192.168.31.0 0.0.0.0 255.255.255.0 U 0 0 0 ethbr0
192.168.39.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr2
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
Output Relevance: From the above output, you can see that the iface(Interface) for 172.18.0.0 is br-2fffe5cd5d9e, which means traffic that needs to go to 172.18.0.0 will go through br-2fffe5cd5d9e which is created by docker for the kind container (this is the node in case of kind cluster).
Now we need to understand how the packet travels from the container interface to the pod with IP 10.244.0.5. The component that handles this is called kube-proxy
So what exactly is kube-proxy:
Kube-Proxy is a network proxy that runs on each node in your cluster, implementing part of the Kubernetes Service concept. kube-proxy maintains network rules on nodes. These network rules allow network communication to your Pods from network sessions inside or outside of your cluster
So, as we can see that kube proxy handles the network rules required to aid the communication to the pods, we will look at the iptables
iptablesis a command line interface used to set up and maintain tables for the Netfilter firewall for IPv4, included in the Linux kernel. The firewall matches packets with rules defined in these tables and then takes the specified action on a possible match. Tables is the name for a set of chains
Command:
# iptables -t nat -L PREROUTING -n
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
KUBE-SERVICES all -- 0.0.0.0/0 0.0.0.0/0 /* kubernetes service portals */
DOCKER_OUTPUT all -- 0.0.0.0/0 172.18.0.1
CNI-HOSTPORT-DNAT all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
# iptables-save | grep PREROUTING
-A PREROUTING -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
Output Relevance:
-A: append new iptable rule -j: jump to the target KUBE-SERVICES: target
The above output appends a new rule for PREROUTING which every network packet will go through first as they try to access any kubernetes service
What is PREROUTING in iptables?
PREROUTING: This chain is used to make any routing related decisions before (PRE) sending any packets
To dig in further we need to go to the target, KUBE-SERVICES for our nginx service.
# iptables -t nat -L KUBE-SERVICES -n| grep nginx
KUBE-SVC-2CMXP7HKUVJN7L6M tcp -- 0.0.0.0/0 10.96.176.241 /* default/nginx cluster IP */ tcp dpt:80
Command:
# iptables -t nat -L KUBE-SVC-2CMXP7HKUVJN7L6M -n
Chain KUBE-SVC-2CMXP7HKUVJN7L6M (2 references)
target prot opt source destination
KUBE-MARK-MASQ tcp -- !10.244.0.0/16 10.96.176.241 /* default/nginx cluster IP */ tcp dpt:80
KUBE-SEP-4IEO3WJHPKXV3AOH all -- 0.0.0.0/0 0.0.0.0/0 /* default/nginx -> 10.244.0.5:80 */
# iptables -t nat -L KUBE-MARK-MASQ -n
Chain KUBE-MARK-MASQ (31 references)
target prot opt source destination
MARK all -- 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
# iptables -t nat -L KUBE-SEP-4IEO3WJHPKXV3AOH -n
Chain KUBE-SEP-4IEO3WJHPKXV3AOH (1 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 10.244.0.5 0.0.0.0/0 /* default/nginx */
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 /* default/nginx */ tcp to:10.244.0.5:80
iptables-save | grep 10.96.176.241
-A KUBE-SERVICES -d 10.96.176.241/32 -p tcp -m comment --comment "default/nginx cluster IP" -m tcp --dport 80 -j KUBE-SVC-2CMXP7HKUVJN7L6M
-A KUBE-SVC-2CMXP7HKUVJN7L6M ! -s 10.244.0.0/16 -d 10.96.176.241/32 -p tcp -m comment --comment "default/nginx cluster IP" -m tcp --dport 80 -j KUBE-MARK-MASQ
As you can see the rules added by kube-proxy helps the packet reach to the destination service.
Now we look at the curl packet journey on minikube. The routing table is looked up to know the destination of the curl packet. The packet then first travels to the virtual bridge 192.168.39.1, created by minikube kvm2 driver, when we created the minikube cluster, on a linux laptop. Then this packet is forwarded to 192.168.39.57, within the minikube VM. We have docker containers running in the VM. Among them, the kube-proxy container creates iptables rules that make sure the packet goes to the correct pod ip, in this case 172.17.0.4.
To begin with the minikube example, we first need to create a minikube cluster on a linux laptop. In this example I'll be using the kvm2 driver option for minikube start command, as default.
minikube start
😄 minikube v1.26.0 on Arch "rolling"
🆕 Kubernetes 1.24.2 is now available. If you would like to upgrade, specify: --kubernetes-version=v1.24.2
✨ Using the kvm2 driver based on existing profile
👍 Starting control plane node minikube in cluster minikube
🏃 Updating the running kvm2 "minikube" VM ...
🐳 Preparing Kubernetes v1.23.3 on Docker 20.10.12 ...
▪ kubelet.housekeeping-interval=5m
🔎 Verifying Kubernetes components...
▪ Using image k8s.gcr.io/ingress-nginx/kube-webhook-certgen:v1.1.1
▪ Using image k8s.gcr.io/ingress-nginx/kube-webhook-certgen:v1.1.1
▪ Using image k8s.gcr.io/ingress-nginx/controller:v1.2.1
▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🔎 Verifying ingress addon...
🌟 Enabled addons: ingress, storage-provisioner, default-storageclass
🏄 Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default
Note: The KVM driver provides a lot of options on customizing the cluster, however that is currently beyond the scope of this guide.
Next we will get the Node IP.
$ kubectl get no -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
minikube Ready control-plane,master 25d v1.23.3 192.168.39.57 <none> Buildroot 2021.02.4 4.19.202 docker://20.10.12
Minikube creates a Virtual Machine using the KVM2 driver(Other drivers such as Virtualbox do exist see minikube start --help for more information ), you should be able to see this with the following output(You may have to use sudo to get this output)
$ virsh --connect qemu:///system list
Id Name State
--------------------------
1 minikube running
or
$ sudo virsh list
Id Name State
--------------------------
1 minikube running
Moving on, simply create a nginx deployment using kubectl.
# kubectl create deployment nginx --image nginx:alpine --port=80
deployment.apps/nginx created
Then we expose this as a NodePort Service.
# kubectl expose deployment/nginx --type=NodePort
service/nginx-new exposed
Command: Now we can see that the service has been exposed.
# kubectl get svc -o wide main
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 25d <none>
nginx-minikube NodePort 10.97.44.4 <none> 80:32007/TCP 45h app=nginx-minikube
Output Relevance: From the above output, we can see that our nginx pod is being exposed as the NodePort service type, and now we can curl the Node IP 192.168.39.57 with the exposed port 32007
Command: The pod has an IP as shown below
# kubectl get po -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-minikube-7546f79bd8-x88bt 1/1 Running 3 (43m ago) 45h 172.17.0.4 minikube <none> <none>
Command: We can use curl on the laptop to view the nginx container that is running on port 32007.
curl 192.168.39.57:32007
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
So, how does this packet travel, lets dive in. We can check the ip interfaces as well subnets for our system is connected to:
$ ifconfig
virbr2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.39.1 netmask 255.255.255.0 broadcast 192.168.39.255
ether 52:54:00:19:29:93 txqueuelen 1000 (Ethernet)
RX packets 5132 bytes 1777099 (1.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 6113 bytes 998530 (975.1 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
virbr0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:48:ee:35 txqueuelen 1000 (Ethernet)
RX packets 23648 bytes 1265196 (1.2 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 40751 bytes 60265308 (57.4 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Output Relevance: From the above output you can see there are two Virtual Bridges created by minikube when we created the cluster on the network. Here, virbr0 is the default NAT network bridge while virbr2 is a isolated network bridge on which the pods run.
Minikube creates a Virtual Machine, to enter the virtual machine we can simple do:
# minikube ssh
The interfaces within the Virtual Machine are as follows.
docker0 Link encap:Ethernet HWaddr 02:42:03:24:26:78
inet addr:172.17.0.1 Bcast:172.17.255.255 Mask:255.255.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:31478 errors:0 dropped:0 overruns:0 frame:0
TX packets:36704 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:3264056 (3.1 MiB) TX bytes:14061883 (13.4 MiB)
eth0 Link encap:Ethernet HWaddr 52:54:00:C9:3A:73
inet addr:192.168.39.57 Bcast:192.168.39.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:8245 errors:0 dropped:9 overruns:0 frame:0
TX packets:3876 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:812006 (792.9 KiB) TX bytes:1044724 (1020.2 KiB)
eth1 Link encap:Ethernet HWaddr 52:54:00:7B:37:79
inet addr:192.168.122.35 Bcast:192.168.122.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:4459 errors:0 dropped:9 overruns:0 frame:0
TX packets:201 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:298528 (291.5 KiB) TX bytes:25813 (25.2 KiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:946772 errors:0 dropped:0 overruns:0 frame:0
TX packets:946772 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:213465460 (203.5 MiB) TX bytes:213465460 (203.5 MiB)
vetha4f1dc5 Link encap:Ethernet HWaddr 3E:1C:FE:C9:75:86
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:10 errors:0 dropped:0 overruns:0 frame:0
TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1413 (1.3 KiB) TX bytes:955 (955.0 B)
vethbf35613 Link encap:Ethernet HWaddr BA:31:7D:AE:2A:BF
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3526 errors:0 dropped:0 overruns:0 frame:0
TX packets:3934 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:342408 (334.3 KiB) TX bytes:380193 (371.2 KiB)
vethe092a51 Link encap:Ethernet HWaddr 8A:37:D3:D9:D9:0E
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:9603 errors:0 dropped:0 overruns:0 frame:0
TX packets:11151 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1199235 (1.1 MiB) TX bytes:5449408 (5.1 MiB)
Output Relevance: Here we have the Virtual Ethernet and we have docker bridges too since docker runs within the Virtual Machine.
When we do a curl to 192.168.39.57:32007 on the laptop the packet first goes to the route table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 192.168.31.1 0.0.0.0 UG 0 0 0 ethbr0
172.17.0.0 0.0.0.0 255.255.0.0 U 0 0 0 docker0
172.18.0.0 0.0.0.0 255.255.0.0 U 0 0 0 br-2fffe5cd5d9e
172.19.0.0 0.0.0.0 255.255.0.0 U 0 0 0 br-be5b544733a3
192.168.31.0 0.0.0.0 255.255.255.0 U 0 0 0 ethbr0
192.168.31.0 0.0.0.0 255.255.255.0 U 0 0 0 ethbr0
192.168.39.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr2
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
Output Relevance: As you can see multiple routes are defined here, of which our Virtual Machine Node IP(192.168.39.57) is also shown in the table, so the packet now knows where it has to go.
With that clear we now know how the packet goes from the laptop to the virtual bridge and then enters the Virtual Machine.
Inside the virtual machine, kube-proxy handles the routing using iptables.
So what exactly is kube-proxy(For those who skipped the kind example):
Kube-Proxy is a network proxy that runs on each node in your cluster, implementing part of the Kubernetes Service concept. kube-proxy maintains network rules on nodes. These network rules allow network communication to your Pods from network sessions inside or outside of your cluster
So, as we can see that kube proxy handles the network rules required to aid the communication to the pods, we will look at the iptables
iptablesis a command line interface used to set up and maintain tables for the Netfilter firewall for IPv4, included in the Linux kernel. The firewall matches packets with rules defined in these tables and then takes the specified action on a possible match. Tables is the name for a set of chains
Command:
# minikube ssh
_ _
_ _ ( ) ( )
___ ___ (_) ___ (_)| |/') _ _ | |_ __
/' _ ` _ `\| |/' _ `\| || , < ( ) ( )| '_`\ /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )( ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)
$ sudo iptables -t nat -L PREROUTING -n
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
KUBE-SERVICES all -- 0.0.0.0/0 0.0.0.0/0 /* kubernetes service portals */
DOCKER all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
$ iptables-save | grep PREROUTING
-A PREROUTING -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
Output Relevance:
-A: append new iptable rule -j: jump to the target KUBE-SERVICES: target
The above output appends a new rule for PREROUTING which every network packet will go through first as they try to access any kubernetes service
What is PREROUTING in iptables?
PREROUTING: This chain is used to make any routing related decisions before (PRE) sending any packets
To dig in further we need to go to the target, KUBE-SERVICES for our nginx service.
# iptables -t nat -L KUBE-SERVICES -n| grep nginx
KUBE-SVC-NRDCJV6H42SDXARP tcp -- 0.0.0.0/0 10.97.44.4 /* default/nginx-minikube cluster IP */ tcp dpt:80
Command:
$ sudo iptables -t nat -L| grep KUBE-SVC-NRDCJV6H42SDXARP
KUBE-SVC-NRDCJV6H42SDXARP tcp -- 0.0.0.0/0 0.0.0.0/0 /* default/nginx-minikube */ tcp dpt:32007
KUBE-SVC-NRDCJV6H42SDXARP tcp -- 0.0.0.0/0 10.97.44.4 /* default/nginx-minikube cluster IP */ tcp dpt:80
$ sudo iptables -t nat -L KUBE-MARK-MASQ -n
Chain KUBE-MARK-MASQ (19 references)
target prot opt source destination
MARK all -- 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
sudo iptables-save | grep 172.17.0.4
-A KUBE-SEP-AHQQ7ZFXMEBNX76B -s 172.17.0.4/32 -m comment --comment "default/nginx-minikube" -j KUBE-MARK-MASQ
-A KUBE-SEP-AHQQ7ZFXMEBNX76B -p tcp -m comment --comment "default/nginx-minikube" -m tcp -j DNAT --to-destination 172.17.0.4:80
As you can see the rules added by kube-proxy helps the packet reach to the destination service.
Connection termination is a type of event that occurs when there are load balancers present, the information for this is quite scarce, however I've found the following article, IBM - Network Termination that describes what it means by connection termination between clients(laptop) and server(load balancer) and the various other services.
The following article on TCP/IP errors has a list of the important tcp timeout errors that we need to know.
| Common TCP/IP errors | Meaning |
|---|---|
| Resource temporarily unavailable. | Self-explanatory. |
| No space is left on a device or system table. | The disk partition is full |
| No route to the host is available. | The routing table doesn't know where to route the packet. |
| Connection was reset by the partner. | This usually means the packet was dropped as soon as it reached the server can be due to a firewall. |
| The connection was timed out. | This indicates the firewall blocking your connection or the connection took too long. |
Layer 7 refers to the seventh and topmost layer of the Open Systems Interconnect (OSI) Model known as the application layer. This is the highest layer which supports end-user processes and applications. Layer 7 identifies the communicating parties and the quality of service between them, considers privacy and user authentication, as well as identifies any constraints on the data syntax. This layer is wholly application-specific.
Since we are doing this on our local laptop, we are going to use the following tools:
- Minikube using KVM driver - The host is linux-based in our example
- Metallb - Baremetal load-balancer.
- KVM / Oracle VirtualBox / VMWare
For setting up metallb, we are going to follow the below steps:
- To begin the installation, we will execute:
minikube start
- To install Metallb, one can install it using the manifest or by using helm, for now we will use the Manifest method:
kubectl apply -f https://raw.githubusercontent.com/metallb/metallb/v0.13.4/config/manifests/metallb-native.yaml
- We need to now configure Metallb, we are using Layer 2 configuration, let's head over to the Metallb Configuration website, here you will see how to setup metallb.
Layer 2 mode does not require the IPs to be bound to the network interfaces of your worker nodes. It works by responding to ARP requests on your local network directly, to give the machine’s MAC address to clients. In order to advertise the IP coming from an IPAddressPool, an L2Advertisement instance must be associated to the IPAddressPool.
- We have modified the IP address pool so that our loadbalancer knows which subnet to choose an IP from.Since we have only one minikube IP we need to modify the code given in the documentation.
Save this as
metallb-config.yaml:
apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
name: first-pool
namespace: metallb-system
spec:
addresses:
# The configuration website show's you this
#- 192.168.10.0/24
#- 192.168.9.1-192.168.9.5
#- fc00:f853:0ccd:e799::/124
# We are going to change this to `minikube ip` as such
- 192.168.39.57/32
Now deploy it using kubectl
kubectl apply -f metallb-config.yaml
- Now that metallb is setup, let's install ingress-nginx on the laptop. Note: We are using the install by manifest option from the Installation manual
kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v1.3.0/deploy/static/provider/cloud/deploy.yaml
or one can also install it using the minikube addons:
minikube addons enable ingress
- Once your Ingress-Nginx controller is created you can run the following commands to see the output of the setup done.
kubectl get pods -n ingress-nginx
NAME READY STATUS RESTARTS AGE
ingress-nginx-admission-create-65bld 0/1 Completed 0 14m
ingress-nginx-admission-patch-rwq4x 0/1 Completed 0 14m
ingress-nginx-controller-6dc865cd86-7c5zd 1/1 Running 0 14m
The Ingress controller creates a Service with the type LoadBalancer and metallb provides the IP address.
kubectl -n ingress-nginx get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
ingress-nginx-controller LoadBalancer 10.108.154.53 192.168.39.223 80:30367/TCP,443:31491/TCP 4d15h
ingress-nginx-controller-admission ClusterIP 10.98.54.3 <none> 443/TCP 4d15h
We will deploy a httpd service in a httpd namespace and create a ingress for it.
First, let's create a namespace.
kubectl create namespace httpd
Next we will create a deployment
kubectl create deployment httpd -n httpd --image=httpd:alpine
Now, In order to create a service, let's expose this deployment
kubectl expose deployment -n httpd httpd --port 80
Let's check the pod that is created
kubectl get po -n httpd
NAME READY STATUS RESTARTS AGE
httpd-fb7fcdc77-w287c 1/1 Running 0 64s
Let's list the services in the httpd namespace
kubectl get svc -n httpd
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
httpd ClusterIP 10.104.111.0 <none> 80/TCP 13s
Once we have this we can now create a n ingress using the following
kubectl -n httpd create ingress httpd --class nginx --rule httpd.dev.leonnunes.com/"*"=httpd:80
The above output, creates an ingress, for us with the rule to match the service if the host is httpd.dev.leonnunes.com. The class here is retrieved from the below command.
To list the ingressclasses use
kubectl get ingressclasses
NAME CONTROLLER PARAMETERS AGE
nginx k8s.io/ingress-nginx <none> 6h49m
The following command shows the ingress created
$ kubectl get ingress -A -o wide
NAMESPACE NAME CLASS HOSTS ADDRESS PORTS AGE
httpd httpd nginx httpd.dev.leonnunes.com 192.168.39.223 80 11d
To test if the rule works we can now do
$ minikube ip
192.168.39.223
$ curl --resolve httpd.dev.leonnunes.com:80:192.168.39.223 httpd.dev.leonnunes.com
<html><body><h1>It works!</h1></body></html>
or
curl -H "Host: httpd.dev.leonnunes.com" 192.168.39.223
We have setup Ingress-Nginx, using nginx as a class and httpd for this example.
In order to display the info on Layer - 7, we have extracted the Layer 7 information from a simple curl request, and then using tcpdump command within the httpd pod we extracted the network packets and opened it using the Wireshark utility.
Below given is the output that is important:
Frame 4: 391 bytes on wire (3128 bits), 391 bytes captured (3128 bits)
Linux cooked capture v2
Internet Protocol Version 4, Src: 172.17.0.4, Dst: 172.17.0.3
Transmission Control Protocol, Src Port: 49074, Dst Port: 80, Seq: 1, Ack: 1, Len: 319
Hypertext Transfer Protocol
GET / HTTP/1.1\r\n
Host: httpd.dev.leonnunes.com\r\n
X-Request-ID: 6e1a790412a0d1615dc0231358dc9c8b\r\n
X-Real-IP: 172.17.0.1\r\n
X-Forwarded-For: 172.17.0.1\r\n
X-Forwarded-Host: httpd.dev.leonnunes.com\r\n
X-Forwarded-Port: 80\r\n
X-Forwarded-Proto: http\r\n
X-Forwarded-Scheme: http\r\n
X-Scheme: http\r\n
User-Agent: curl/7.84.0\r\n
Accept: */*\r\n
\r\n
[Full request URI: http://httpd.dev.leonnunes.com/]
[HTTP request 1/1]
[Response in frame: 6]
The above output shows the information that the httpd pod recieves. The curl command sends the host header, Host: httpd.dev.leonnunes.com, to the nginx controller, that then matches the rule and sends the information to the right controller
The following output shows what is sent via the laptop.
curl --resolve httpd.dev.leonnunes.com:80:192.168.39.57 -H "Host: httpd.dev.leonnunes.com" 192.168.39.57 -vL
* Added httpd.dev.leonnunes.com:80:192.168.39.57 to DNS cache
* Trying 192.168.39.57:80...
* Connected to 192.168.39.57 (192.168.39.57) port 80 (#0)
> GET / HTTP/1.1
> Host: httpd.dev.leonnunes.com
> User-Agent: curl/7.84.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Date: Mon, 22 Aug 2022 16:05:27 GMT
< Content-Type: text/html
< Content-Length: 45
< Connection: keep-alive
< Last-Modified: Mon, 11 Jun 2007 18:53:14 GMT
< ETag: "2d-432a5e4a73a80"
< Accept-Ranges: bytes
<
<html><body><h1>It works!</h1></body></html>
* Connection #0 to host 192.168.39.57 left intact
As you can see from the above output there are several headers added to the curl output after it reaches the httpd pod, these headers are added by the Ingress Nginx Controller.
- https://www.cisco.com/en/US/docs/security/vpn5000/manager/reference/guide/appA.html
- http://web.stanford.edu/class/cs101/
- https://www.geeksforgeeks.org/basics-computer-networking/
- Subnetting
- https://www.youtube.com/playlist?list=PLhfrWIlLOoKPc2RecyiM_A9nf3fUU3e6g
- https://www.youtube.com/watch?v=S7MNX_UD7vY&list=PLIhvC56v63IJVXv0GJcl9vO5Z6znCVb1P
- Docker in Docker
- Docker/Containers
- Containers
- mtr - Tracing the packet from the source to destination
- tcpdump - Monitor packets
- wireshark - Read/Sniff packets
- nslookup - Lookup Nameservers
- netstat - List network details
- curl - Curl a website from the command line
- ifconfig/ip - Show ip address configuration
- dig - Query Nameservers
- ipcalc - Calculate IP addresses
- Advanced Tools for troubleshooting
- Netshoot - Troubleshoot Networks
- Cluster Creation tools