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Networking

Ipv4

All networking in Rahti uses IPv4. All IPs in this document and Rahti's system itself are ipv4 only, no ipv6 IP is used.

Namespaces

Rahti is divided in Namespaces. Depending on the context, namespaces can be referred as Projects. Every object in Rahti must belong to and run inside a namespace. From a networking point of view, namespaces provide an isolated VLAN to everything that runs inside it, notably to Pods, Services and Routes.

Rahti Networking

Pods

Pods are the basic unit in Kubernetes. They accommodate one or more containers that contain the software and the environment needed to run an application. Each Pod has a private IP, which is only reachable from inside the namespace/VLAN. It is not advisable to use these Pod IPs directly in applications, they are meant to be used by Services. This is because not only other Pods in other namespaces may share this private IP, but more importantly, when a Pod is recreated it will get a new IP.

For example, if we deploy the nginx image in a Pod. This Pod will get a random private IP like 10.1.1.200. Any unprivileged port (>=1024) that the image exports, like for example 8081, will be reachable in that IP. A Pod will fail to start if it tries to export a privileged port ([0-1023]). If the Pod is killed, normally due to a change in its configuration, but also possibly due to unexpected reasons like hardware failure, a new Pod with a different IP will be created, like for example 10.1.1.140. These IPs will respond to traffic from within the namespace only. If we set up a Pod that will query the first IP (10.1.1.200), it will obviously stop working at the moment of the recreation of the Pod associated with it. This is why we use services.

Services

Services (also abbreviated svc) provide a stable private IP to one or more Pods. This IP will act as a load balancer, distributing the traffic load between the Pods behind it. For this, the service will make sure to keep an updated list of IPs so requests are only sent to valid ones.

Services are built to export one or more ports, and they also provide an internal DNS name. Any of these names are valid and will resolve to the same service IP:

  • <service_name>, e.g., nginx.
  • <service_name>.<namespace>, e.g., ngin.fenic
  • and <service_name>.<namespace>.svc.cluster.local, e.g., nginx.fenic.svc.cluster.local.

In the same manner than Pods, Rahti Services can only be reached from inside the namespace they run, any request from another namespace will be able to resolve the DNS into an IP, but it will never connect. Another feature of services is that they can forward requests from one port to another target port (ex: 80 to 8080). This is useful in Rahti as Pods cannot listen on privileged ports (<1024).

Services are used to both internal and external connections. For example, if we have one or more MongoDB database replicas of the same pod running in the fenic namespace, and they export port 27017. We can create a service called mongo associated with the pods under the same name. Then we can launch nginx Pods that run a Python application which will use the URL to connect to the database. When connections to the service are attempted, one of the mongo pods will be selected to serve the data request.

nginx and Mongo

Routes

Routes are the OpenShift equivalent of Ingress in vanilla Kubernetes, they expose a single port of a single Service object to traffic from outside the namespace and the Internet, via HTTP/HTTPS only. If the route is configured to provide no encrypted HTTP traffic, the pods associated should talk in HTTP non encrypted traffic. If the route is configured to provide TLS/HTTPS secure traffic, several options are available regarding the Route encryption:

  • Edge, this is the default and the simplest to configure. The Route provides the certificate, which is stored in the Route object itself. The traffic is decrypted and the Pod is contacted using plain text un-encrypted HTTPD traffic.
  • Passthrough is when the encryption is delegated to the pod, which must listen for TLS/HTTPS traffic and provide the certificate the client will receive.
  • Re-encrypt, this is a mixture of two previous options, the Route will provide a certificate, but it will connect to the Pod using TLS/HTTPS and expect a valid certificate for the domain name of the service. The client will still get the certificate stored by the Route. This is for example used when the internal network between nodes in the cluster is not considered secure enough and we still want the Route to control the certificates that the client will get. Also in some rare applications is not possible to disable TLS in the Pods.

Route Options

A Route can also be configured to provide a HTTP/302 redirection from port 80 to 443. It is also possible to serve the same content in both ports, or to not serve anything at all in the un secure 80 port.

An important limitation for Rahti is that only the HTTP/80 and HTTPS/443 ports are exposed for incoming traffic, and they only can serve HTTPD protocol requests. Internally to a namespace, any port and protocol is supported, this means we can connect an application to a database with no issues, but we will never be able to expose that database to outside traffic. This is due to the fact that the same incoming virtual IP is shared with all the incoming traffic in Rahti's HAProxy load balancers. Name-based virtual hosts are used to redirect the traffic to the correct Route. Other protocols that are not HTTPD, do not have this feature and will need a dedicated IP/port pair to work.

Rahti provides a range of pre-created domain names, XXXX.rahtiapp.fi where XXXX can be any combination of letters, numbers and dashes. These pre-created domain names also come with a valid TLS certificate.

$ dig hola.rahtiapp.fi CNAME | grep 'ANSWER SECTION' -A 1
;; ANSWER SECTION:
hola.rahtiapp.fi.   113 IN  CNAME   rahtiapp.fi.

$ dig moi.rahtiapp.fi CNAME | grep 'ANSWER SECTION' -A 1
;; ANSWER SECTION:
moi.rahtiapp.fi.    96  IN  CNAME   rahtiapp.fi.

$ dig rahtiapp.fi A |  grep 'ANSWER SECTION' -A 1
;; ANSWER SECTION:
rahtiapp.fi.        328 IN  A   193.167.189.101

Every single pre-created domain name is configured as a CNAME that points to rahtiapp..fi, which itself points to one of the HAProxy load balancers.

Any other domain name is possible, but the DNS and the certificates must be managed by the customer.

  • For the DNS, a CNAME pointing to rahtiapp.fi or in cases that this is not possible, directly the A record containing the IP of rahtiapp.fi has to be configured. The way this needs to be configured depends on the register of the DNS record.

  • Any certificate provider can be used, like for example use the free certificates provided by the Let's Encrypt controller.

Another aspect of routes is the IP white listing feature, ie: only allowing a range of IPs to access the route. This is controlled by creating an annotation in the Route object with the key haproxy.router.openshift.io/ip_whitelist, and by setting the value to a space separated list of IPs and or IP ranges.

  • This first example will white list a range of IPs (193.166.[0-255].[1-254]):
oc annotate route <route_name> haproxy.router.openshift.io/ip_whitelist='193.166.0.0/16'
  • This other example will white list only a specific IP:
oc annotate route <route_name> haproxy.router.openshift.io/ip_whitelist='188.184.9.236'
  • And this example will combine both:
oc annotate route <route_name> haproxy.router.openshift.io/ip_whitelist='193.166.0.0/15 193.167.189.25'

Egress IPs

The IP for all outgoing customer traffic is 193.167.189.25. Any pod that runs in Rahti will use by default this IP to reach anything located outside Rahti or a Route. It is possible, for selected namespaces that need it, to configure a dedicated IP. Each request is reviewed individually due to the fact that there is a limited pool of virtual IPs available.

Last edited Fri Aug 27 2021