Get started with OpenShift

A short introduction: accessing the cluster

1. Install Telepresence (see below).

2. Run a service in the cluster:

   Terminal

   copied
   $ oc run myservice --image=datawire/hello-world --port=8000 --expose
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   $ oc get service myservice
   NAME        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
   myservice   10.0.0.12    <none>        8000/TCP   1m
   

   It may take a minute or two for the pod running the server to be up and running, depending on how fast your cluster is.

3. You can now run a local process using Telepresence that can access that service, even though the process is local but the service is running in the OpenShift cluster:

   Terminal

   copied
   $ telepresence --run curl http://myservice:8000/
   Hello, world!
   

   (This will not work if the hello world pod hasn't started yet... if so, try again.)

curl got access to the cluster even though it's running locally! In the more extended tutorial that follows you'll see how you can also route traffic to a local process from the cluster.

A longer introduction: exposing a service to the cluster

Debugging a service locally with Telepresence

Imagine you have a service running in a staging cluster, and someone reports a bug against it.

In order to figure out the problem you want to run the service locally... but the service depends on other services in the cluster, and perhaps on cloud resources like a database.

In this tutorial you'll see how Telepresence allows you to debug your service locally.

We'll use the telepresence command line tool to swap out the version running in the staging cluster for a debug version under your control running on your local machine.

Telepresence will then forward traffic from OpenShift to the local process.

You should start a new application and publicly expose it:

Important: It might be necessary to define security context constraint in order for Telepresence to run privileged containers. Execute following using an account with sufficient permission (i.e. for local cluster login first as system:admin):

The service will be running once the following shows a pod with Running status that doesn't have "deploy" in its name:

To find the address of the resulting app you can run:

In the above output the address is http://example.openshiftsapps.com, but you will get a different value. It may take a few minutes before this route will be live; in the interim you will get an error page. If you do wait a minute and try again.

Once you know the address you can store its value (don't forget to replace this with the real address!):

And you send it a query and it will be served by the code running in your cluster:

Swapping your deployment with Telepresence

Important Starting telepresence the first time may take a little while, since $OpenShift needs to download the server-side image.

At this point you want to switch to developing the service locally, replace the version running on your cluster with a custom version running on your laptop.

To simplify the example we'll just use a simple HTTP server that will run locally on your laptop:

We want to expose this local process so that it gets traffic from $OpenShift, replacing the existing \`hello-world\` deployment.

Important: you're about to expose a web server on your laptop to the Internet.

This is pretty cool, but also pretty dangerous!

Make sure there are no files in the current directory that you don't want shared with the whole world.

Here's how you should run telepresence (you should make sure you're still in the /tmp/telepresence-test directory you created above):

This does three things:

* Starts a VPN-like process that sends queries to the appropriate DNS and IP ranges to the cluster.

* --swap-deployment tells Telepresence to replace the existing hello-world pod with one running the Telepresence proxy. On exit, the old pod will be restored.

* --run tells Telepresence to run the local web server and hook it up to the networking proxy.

As long as you leave the HTTP server running inside telepresence it will be accessible from inside the $OpenShift cluster.

You've gone from this...

...to this:

We can now send queries via the public address of the \`Service\` we created, and they'll hit the web server running on your laptop instead of the original code that was running there before.

Wait a few seconds for the Telepresence proxy to startup; you can check its status by doing:

Once you see that the new pod is in \`Running\` state you can use the new proxy to connect to the web server on your laptop:

Finally, let's kill Telepresence locally so you don't have to worry about other people accessing your local web server by bringing it to the foreground and hitting Ctrl-C:

Now if we wait a few seconds the old code will be swapped back in.

Again, you can check status of swap back by running:

When the new pod is back to \`Running\` state you can see that everything is back to normal:

> What you've learned: Telepresence lets you replace an existing deployment with a proxy that reroutes traffic to a local process on your machine.

> This allows you to easily debug issues by running your code locally, while still giving your local process full access to your staging or testing cluster.

Now it's time to clean up the service:

Telepresence can do much more than this: see the reference section of the documentation, on the top-left, for details.

Still have questions? Ask in our Slack chatroom or file an issue on GitHub