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From the Kubernetes documentation:
A Kubernetes service is an abstraction which defines a logical set of pods and a
policy by which to access them - sometimes called a micro-service. The goal of
services is to provide a bridge for non-Kubernetes-native applications to access
backends without the need to write code that is specific to Kubernetes. A
service offers clients an IP and port pair which, when accessed, redirects to
the appropriate backends. The set of pods targetted is determined by a label
selector.
If you think back to the simple pod we created earlier, there was a "label":
"labels": {
"name": "hello-openshift"
},
Now, let's look at a service definition:
{
"kind": "Service",
"apiVersion": "v1",
"metadata": {
"name": "hello-service"
},
"spec": {
"selector": {
"name":"hello-openshift"
},
"ports": [
{
"protocol": "TCP",
"port": 8888,
"targetPort": 8080
}
]
}
}
The service has a selector element. In this case, it is a key:value pair of
app:hello-openshift. If you looked at the output of oc get pods on your
master, you saw that the hello-openshift pod has a label:
name=hello-openshift
The definition of the service tells Kubernetes that any pods with the label "name=hello-openshift" are associated, and should have traffic distributed amongst them. In other words, the service provides an abstraction layer, and is the input point to reach all of the pods. Generally speaking, pod containers should not bind directly to ports on the host. We'll see more about this later.
To really be useful, we want to make our application accessible via a FQDN, and that is where the routing tier comes in.
We can create a service from the command line with JSON or YAML just like we
created the pod. The hello-service.json file has the service definition we saw
above. Go ahead and create the service:
oc create -f hello-service.json
oc describe will usually tell us some interesting things about a resource.
Let's look at the service we just created:
oc describe service hello-service
Name: hello-service
Labels: <none>
Selector: name=hello-openshift
Type: ClusterIP
IP: 172.30.42.80
Port: <unnamed> 8888/TCP
Endpoints: <none>
Session Affinity: None
No events.
We see that the service was assigned an IP address. This IP address will persist for the life of the service. This can make it very convenient for other people to actually use our service/application within an OpenShift environment. They don't have to keep track of our pods manually.
Right now there are no endpoints in the service -- there are no matching pods. Let's fix that.
We can use our quota test file to launch some pods again. These pods all have the label "name:hello-openshift". When we create them, and they finally come to life, we should see them come up in the service's endpoint list.
Go ahead and create them again:
oc create -f hello-quota.json
You'll still get the error about quota -- we're still trying to create 4 pods when we're only allowed 3.
Wait a few moments and then describe your service:
oc describe service hello-service
Name: hello-service
Labels: <none>
Selector: name=hello-openshift
Type: ClusterIP
IP: 172.30.42.80
Port: <unnamed> 8888/TCP
Endpoints: 10.1.0.6:8080,10.1.1.3:8080,10.1.1.4:8080
Session Affinity: None
No events.
Now we have several endpoints behind this service. If you look at the web console, you'll see these 3 pods all associated with our hello-service.
If you do a curl of the service, you should see your application (remember to substitute whatever service IP matches your environment):
curl 172.30.42.80:8888
Hello OpenShift!
This is well and good, but what if I want to access this application from outside the OpenShift environment?
The OpenShift routing tier is how FQDN-destined traffic enters the OpenShift
environment so that it can ultimately reach pods. In a simplification of the
process, the openshift3/ose-haproxy-router container we will create below
is a pre-configured instance of HAProxy as well as some of the OpenShift
framework. The OpenShift instance running in this container watches for route
resources on the OpenShift master.
Here is an example route resource JSON definition:
{
"kind": "Route",
"apiVersion": "v1",
"metadata": {
"name": "hello-openshift-route"
},
"spec": {
"host": "hello-openshift.cloudapps.example.com",
"to": {
"kind": "Service",
"name": "hello-openshift-service"
},
"tls": {
"termination": "edge"
}
}
}
When the oc command is used to create this route, a new instance of a route
resource is created inside OpenShift's data store. This route resource is
affiliated with a service.
The HAProxy/Router is watching for changes in route resources. When a new route is detected, an HAProxy pool is created. When a change in a route is detected, the pool is updated.
This HAProxy pool ultimately contains all pods that are in a service. Which
service? The service that corresponds to the to directive that you
see above.
You'll notice that the definition above specifies TLS edge termination. This means that the router should provide this route via HTTPS. Because we provided no certificate info, the router will provide its default SSL certificate when the user connects. Because this is edge termination, user connections to the router will be SSL encrypted but the connection between the router and the pods is unencrypted.
It is possible to utilize various TLS termination mechanisms, and more details is provided in the router documentation:
https://docs.openshift.com/enterprise/3.0/architecture/core_concepts/routes.html#secured-routes
We'll see this edge termination in action shortly.
In order to serve a valid certificate for secure access to applications in our cloud domain, we will need to create a key and wildcard certificate that the router will use by default for any routes that do not specify a key/cert of their own. OpenShift supplies a command for creating a key/cert signed by the OpenShift CA which we will use.
On the master, as root:
CA=/etc/openshift/master
oadm create-server-cert --signer-cert=$CA/ca.crt \
--signer-key=$CA/ca.key --signer-serial=$CA/ca.serial.txt \
--hostnames='*.cloudapps.example.com' \
--cert=cloudapps.crt --key=cloudapps.key
Now we need to combine cloudapps.crt and cloudapps.key with the CA into
a single PEM format file that the router needs in the next step.
cat cloudapps.crt cloudapps.key $CA/ca.crt > cloudapps.router.pem
Make sure you remember where you put this PEM file.
The router is the ingress point for all traffic destined for OpenShift v3 services. It currently supports only HTTP(S) traffic (and "any" TLS-enabled traffic via SNI). While it is called a "router", it is essentially a proxy.
The openshift3/ose-haproxy-router container listens on the host network
interface, unlike most containers that listen only on private IPs. The router
proxies external requests for route names to the IPs of actual pods identified
by the service associated with the route.
OpenShift's admin command set enables you to deploy router pods automatically.
Perform the following comands as root.
Let's try to create a router:
oadm router
error: router could not be created; you must specify a .kubeconfig file path containing credentials for connecting the router to the master with --credentials
Just about every form of communication with OpenShift components is secured by
SSL and uses various certificates and authentication methods. Even though we set
up our .kubeconfig for the root user, oadm router is asking us what
credentials the router should use to communicate with the master. We also need
to specify the router image, since the tooling defaults to upstream/origin:
oadm router --dry-run \
--credentials=/etc/openshift/master/openshift-router.kubeconfig
Adding that would be enough to allow the command to proceed, but if we want
this router to work for our environment, we also need to specify the
router image (the tooling defaults to upstream/origin otherwise) and we need
to supply the wildcard cert/key that we created for the cloud domain. Since the
router command will create all of the resources in the default project, and
the default project has the nodeSelector for the infra region, the router
pod will land there.
oadm router --default-cert=cloudapps.router.pem \
--credentials=/etc/openshift/master/openshift-router.kubeconfig \
--images='registry.access.redhat.com/openshift3/ose-${component}:${version}'
If this works, you'll see some output:
password for stats user admin has been set to Cwwk96Huso
deploymentconfigs/router
services/router
Note: You will have to reference the absolute path of the PEM file if you did not run this command in the folder where you created it.
Note: You will want to keep that password handy. But you can get it by looking at the DeploymentConfiguration later. Don't worry.
Let's check the pods as root:
oc get pods
In the output, you should see the router pod status change to "running" after a few moments (it may take up to a few minutes):
NAME READY REASON RESTARTS AGE
router-1-rt6qk 1/1 Running 0 20s
If you describe the router pod, you will see that it is running on the master:
oc describe pod router-1-rt6qk
Name: router-1-rt6qk
Image(s): registry.access.redhat.com/openshift3/ose-haproxy-router:v0.6.1.0
Host: ose3-master.example.com/192.168.133.2
Labels: deployment=router-1,deploymentconfig=router,router=router
Status: Running
IP: 10.1.0.4
Replication Controllers: router-1 (1/1 replicas created)
Containers:
router:
Image: registry.access.redhat.com/openshift3/ose-haproxy-router:v0.6.1.0
State: Running
Started: Wed, 17 Jun 2015 14:49:42 -0400
Ready: True
Restart Count: 0
Conditions:
Type Status
Ready True
Events:
FirstSeen LastSeen Count From SubobjectPath Reason Message
Wed, 17 Jun 2015 14:49:40 -0400 Wed, 17 Jun 2015 14:49:40 -0400 1 {scheduler } scheduled Successfully assigned router-1-rt6qk to ose3-master.example.com
Wed, 17 Jun 2015 14:49:40 -0400 Wed, 17 Jun 2015 14:49:40 -0400 1 {kubelet ose3-master.example.com} implicitly required container POD pulled Successfully pulled image "openshift3/ose-pod:v0.6.1.0"
Wed, 17 Jun 2015 14:49:41 -0400 Wed, 17 Jun 2015 14:49:41 -0400 1 {kubelet ose3-master.example.com} implicitly required container POD created Created with docker id 9e3c20ad9e356e9495004004b81b19d3eaaa721f42ee07073380efaa9047b45a
Wed, 17 Jun 2015 14:49:41 -0400 Wed, 17 Jun 2015 14:49:41 -0400 1 {kubelet ose3-master.example.com} implicitly required container POD started Started with docker id 9e3c20ad9e356e9495004004b81b19d3eaaa721f42ee07073380efaa9047b45a
Wed, 17 Jun 2015 14:49:42 -0400 Wed, 17 Jun 2015 14:49:42 -0400 1 {kubelet ose3-master.example.com} spec.containers{router} created Created with docker id f891a779c18ed960ae27d630e7df2061531533ead6df4b262d642c2d0a3902ef
Wed, 17 Jun 2015 14:49:42 -0400 Wed, 17 Jun 2015 14:49:42 -0400 1 {kubelet ose3-master.example.com} spec.containers{router} started Started with docker id f891a779c18ed960ae27d630e7df2061531533ead6df4b262d642c2d0a3902ef
In the very beginning of the documentation, we indicated that a wildcard DNS entry is required and should point at the master. When the router receives a request for an FQDN that it knows about, it will proxy the request to a pod for a service. But, for that FQDN request to actually reach the router, the FQDN has to resolve to whatever the host is where the router is running. Remember, the router is bound to ports 80 and 443 on the host interface. Our wildcard DNS entry points to the public IP address of the master, and the configuration of our default project ensures that the router will only ever land in the infra region. Since there is only one node in the infra region (the master), we know we can point the wildcard DNS entry at the master and we'll be all set.
For a true HA implementation, one would want multiple "infra" nodes and multiple, clustered router instances. Please see the "high availability" documentation for more information on how tihs can be achieved:
https://docs.openshift.com/enterprise/3.0/admin_guide/high_availability.html
Haproxy provides a stats page that's visible on port 1936 of your router host.
The username is admin and the password was displayed to you when you created
the router. If you forgot it, you can find it by describeing the deployment
configuration of the router:
oc describe dc router
To make the stats port acessible publicly, you will need to open it on your master:
iptables -I OS_FIREWALL_ALLOW -p tcp -m tcp --dport 1936 -j ACCEPT
You will also want to add this rule to /etc/sysconfig/iptables as well to keep
it across reboots. However, don't restart the iptables service, as this would
destroy the rules that have already been created by Openshift. Use the
iptables command to change rules on a live system.
Feel free to not open this port if you don't want to make this accessible, or if you only want it accessible via port fowarding, etc.
Note: Unlike OpenShift v2 this router is not specific to a given project, as such it's really intended to be viewed by OpenShift admins rather than project admins or application developers.
Ensure that port 1936 is accessible and visit:
http://admin:$YOURPASSWORDHERE@ose3-master.example.com:1936
to view your router stats.
If you've been following along closely, right now you have three pods that all belong to a service. We previously asked the question "How can we make this service accessible to users outside of OpenShift?" and the answer was via the routing layer.
Let's go ahead and actually create a route for this service by exposeing it.
As joe, execute the following:
oc expose service hello-service -l name=hello-openshift
Wait a couple of moments, and then look at the routes with the following:
oc get route
NAME HOST/PORT PATH SERVICE LABELS
hello-service hello-service.demo.cloudapps.example.com hello-service name=hello-openshift
The expose command created a route for us. The -l name=hello-openshift added
a label to this route resource, too. Since we didn't specify an FQDN with the
command, OpenShift programmatically generates our route with the format of:
<service_name>.<project_name>.<cloud_domain>
In our master's config we had configured the routing subdomain as
cloudapps.example.com. The project we're working in is demo and the service
name was hello-service. That's how the HOST/PORT was chosen.
If you configured your wildcard DNS correctly, you should be able to curl this and see your application:
curl hello-service.demo.cloudapps.example.com
Hello OpenShift!
Hooray!
The previous steps essentially build an "application" from scratch with lots of
individual JSON components. However, we can have a single JSON List that
describes all of the resources we want to create.
First, let's delete everything we previously created:
oc delete all -l name=hello-openshift
You will see something like:
routes/hello-service
services/hello-service
pods/hello-openshift-1
pods/hello-openshift-2
pods/hello-openshift-3
Since everything we created had a specific label, we can also delete everything with that specific label. Using labels makes it very easy to find and operate on resources in OpenShift.
Don't forget -- the materials are in ~/training/content.
The following is a complete definition for a pod with a corresponding service and a corresponding route. It also includes a deployment configuration.
{
"kind": "List",
"apiVersion": "v1",
"metadata": {
"name": "hello-service-complete-example"
},
"items": [
{
"kind": "Service",
"apiVersion": "v1",
"metadata": {
"name": "hello-openshift-service"
},
"spec": {
"selector": {
"name": "hello-openshift"
},
"ports": [
{
"protocol": "TCP",
"port": 27017,
"targetPort": 8080
}
]
}
},
{
"kind": "Route",
"apiVersion": "v1",
"metadata": {
"name": "hello-openshift-route"
},
"spec": {
"host": "hello-openshift.cloudapps.example.com",
"to": {
"name": "hello-openshift-service"
},
"tls": {
"termination": "edge"
}
}
},
{
"kind": "DeploymentConfig",
"apiVersion": "v1",
"metadata": {
"name": "hello-openshift"
},
"spec": {
"strategy": {
"type": "Recreate",
"resources": {}
},
"triggers": [
{
"type": "ConfigChange"
}
],
"replicas": 1,
"selector": {
"name": "hello-openshift"
},
"template": {
"metadata": {
"creationTimestamp": null,
"labels": {
"name": "hello-openshift"
}
},
"spec": {
"containers": [
{
"name": "hello-openshift",
"image": "openshift/hello-openshift:v0.4.3",
"ports": [
{
"name": "hello-openshift-tcp-8080",
"containerPort": 8080,
"protocol": "TCP"
}
],
"resources": {
"limits": {
"cpu": "10m",
"memory": "16Mi"
}
},
"terminationMessagePath": "/dev/termination-log",
"imagePullPolicy": "IfNotPresent",
"capabilities": {},
"securityContext": {
"capabilities": {},
"privileged": false
},
"livenessProbe": {
"tcpSocket": {
"port": 8080
},
"timeoutSeconds": 1,
"initialDelaySeconds": 10
}
}
],
"restartPolicy": "Always",
"dnsPolicy": "ClusterFirst",
"serviceAccount": "",
"nodeSelector": {
"region": "primary"
}
}
}
}
}
]
}
In the JSON above:
- There is a pod whose containers have the label
name=hello-openshift-labeland the nodeSelectorregion=primary - There is a service:
- with the id
hello-openshift-service - with the selector
name=hello-openshift
- with the id
- There is a route:
- with the FQDN
hello-openshift.cloudapps.example.com - with the
spectoname=hello-openshift-service
- with the FQDN
If we work from the route down to the pod:
- The route for
hello-openshift.cloudapps.example.comhas an HAProxy pool - The pool is for any pods in the service whose ID is
hello-openshift-service, via theserviceNamedirective of the route. - The service
hello-openshift-serviceincludes every pod who has a labelname=hello-openshift-label - There is a single pod with a single container that has the label
name=hello-openshift-label
If your domain is different, you will need to edit the JSON before trying to create the objects.
Logged in as joe, go ahead and use oc to create everything:
oc create -f test-complete.json
You should see something like the following:
services/hello-openshift-service
routes/hello-openshift-route
deploymentconfigs/hello-openshift
You can verify this with other oc commands:
oc get pods
oc get services
oc get routes
oc get rc
oc get dc
OpenShift provides a handy tool, oc status, to give you a summary of
common resources existing in the current project:
oc status
In project OpenShift 3 Demo (demo)
service hello-openshift-service (172.30.252.29:27017 -> 8080)
hello-openshift deploys docker.io/openshift/hello-openshift:v0.4.3
#1 deployed about a minute ago - 1 pod
To see more information about a Service or DeploymentConfig, use 'oc describe service <name>' or 'oc describe dc <name>'.
You can use 'oc get all' to see lists of each of the types described above.
oc status does not yet show bare pods or routes. The output will be
more interesting when we get to builds and deployments.
Services are not externally accessible without a route being defined, because they always listen on "local" IP addresses (eg: 172.x.x.x). However, if you have access to the OpenShift environment, you can still test a service.
oc get services
NAME LABELS SELECTOR IP(S) PORT(S)
hello-openshift-service name=hello-openshift name=hello-openshift 172.30.185.26 27017/TCP
We can see that the service has been defined based on the JSON we used earlier.
If the output of oc get pods shows that our pod is running, we can try to
access the service:
curl `oc get services | grep hello-openshift | awk '{print $4":"$5}' | sed -e 's/\/.*//'`
Hello OpenShift!
This is a good sign! It means that, if the router is working, we should be able to access the service via the route.
Verifying the routing is a little complicated, but not terribly so. Since we
specified that the router should land in the "infra" region, we know that its
Docker container is on the master. Log in there as root.
We can use oc exec to get a bash interactive shell inside the running
router container. The following command will do that for us:
oc exec -it -p $(oc get pods | grep router | awk '{print $1}' | head -n 1) /bin/bash
You are now in a bash session inside the container running the router. We'll
talk more about oc exec later. For now, just realize that OpenShift is letting
you operate an interactive process inside a running Docker container in the
OpenShift environment.
Since we are using HAProxy as the router, we can cat the routes.json file:
cat /var/lib/containers/router/routes.json
If you see some content that looks like:
"demo/hello-openshift-service": {
"Name": "demo/hello-openshift-service",
"EndpointTable": [
{
"ID": "10.1.2.6:8080",
"IP": "10.1.2.6",
"Port": "8080",
"TargetName": "hello-openshift-1-ehacs"
}
],
"ServiceAliasConfigs": {
"demo-hello-openshift-route": {
"Host": "hello-openshift.cloudapps.example.com",
"Path": "",
"TLSTermination": "edge",
"Certificates": {
"hello-openshift.cloudapps.example.com": {
"ID": "demo-hello-openshift-route",
"Contents": "",
"PrivateKey": ""
}
},
"Status": "saved"
}
}
}
You know that "it" worked -- the router watcher detected the creation of the route in OpenShift and added the corresponding configuration to HAProxy.
Go ahead and exit from the container.
bash-4.2$ exit
As joe, you can reach the route securely and check that it is using the right
certificate:
curl --cacert /etc/openshift/master/ca.crt \
https://hello-openshift.cloudapps.example.com
Hello OpenShift!
And:
openssl s_client -connect hello.cloudapps.example.com:443 \
-CAfile /etc/openshift/master/ca.crt
CONNECTED(00000003)
depth=1 CN = openshift-signer@1430768237
verify return:1
depth=0 CN = *.cloudapps.example.com
verify return:1
[...]
Since we used OpenShift's CA to create the wildcard SSL certificate, and since that CA is not "installed" in our system, we need to point our tools at that CA certificate in order to validate the SSL certificate presented to us by the router. With a CA or all certificates signed by a trusted authority, it would not be necessary to specify the CA everywhere.
If you are interested, and you exposed the router admin port, you can visit the status page and see that you will have some session information for your route.
Take a moment to look in the web console to see if you can find everything that was just created.