So far we‘ve covered how to configure and compose entities. There’s a large library of blueprints available, but there are also times when you'll want to write your own.
For complex use cases, you can write JVM, but for many common situations, some of the highly-configurable blueprints make it easy to write in YAML, including bash
and Chef.
bash
The following blueprint shows how a simple script can be embedded in the YAML (the |
character is special YAML which makes it easier to insert multi-line text):
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat.yaml %} {% endhighlight %}
This starts a simple nc
listener on port 4321 which will respond hello
to the first session which connects to it. Test it by running telnet localhost 4321
or opening http://localhost:4321
in a browser.
Note that it only allows you connect once, and after that it fails. This is deliberate! We'll repair this later in this example. Until then however, in the Applications view you can click the server, go to the Effectors
tab, and click restart
to bring if back to life.
This is just a simple script, but it shows how any script can be easily embedded here, including a script to download and run other artifacts. Many artifacts are already packaged such that they can be downloaded and launched with a simple script, and VanillaSoftwareProcess
can also be used for them.
We can specify a download.url
which downloads an artifact (and automatically unpacking TAR, TGZ, and ZIP archives) before running launch.command
relative to where that file is installed (or unpacked), with the default launch.command
being ./start.sh
.
So if we create a file /tmp/netcat-server.tgz
containing just start.sh
in the root which consists of the two lines in the previous example, we can instead write our example as:
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-file.yaml %} {% endhighlight %}
If you're deploying to a cloud machine, a firewall might block the port 4321. We can tell Brooklyn to open this port explicitly by specifying inboundPorts: [ 4321 ]
; however a more idiomatic way is to specify a config ending with .port
, such as:
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-port.yaml %} {% endhighlight %}
The regex for ports to be opened can be configured using the config inboundPorts.configRegex
(which has .*\.port
as the default value).
Config keys of type org.apache.brooklyn.api.location.PortRange
(aka port
) have special behaviour: when configuring, you can use range notation 8000-8100
or 8000+
to tell Brooklyn to find one port matching; this is useful when ports might be in use. In addition, any such config key will be opened, irrespective of whether it matches the inboundPorts.configRegex
. To prevent any inferencing of ports to open, you can set the config inboundPorts.autoInfer
to false
.
Note that in the example above, netcat.port
must be specified in a brooklyn.config
block. This block can be used to hold any config (including for example the launch.command
), but for convenience Brooklyn allows config keys declared on the underlying type to be specified up one level, alongside the type. However config keys which are not declared on the type must be declared in the brooklyn.config
block.
We can define config keys to be presented to the user using the brooklyn.parameters
block:
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-port-parameter.yaml %} {% endhighlight %}
The example above will allow a user to specify a message to send back and the port where netcat will listen. The metadata on these parameters is available at runtime in the UI and through the API, and is used when populating a catalog.
The example also shows how these values can be passed as environment variables to the launch command. The $brooklyn:config(...)
function returns the config value supplied or default. For the type port
, an attribute sensor is also created to report the actual port used after port inference, and so the $brooklyn:attributeWhenReady(...)
function is used. (If $brooklyn:config("netcat.port")
had been used, 4321+
would be passed as NETCAT_PORT
.)
This gives us quite a bit more power in writing our blueprint:
4321+
syntax enables Brooklyn to assign them different portsThe Catalog tab allows you to add blueprints which you can refer to in other blueprints. In that tab, click + then YAML, and enter the following:
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-catalog.bom %} {% endhighlight %}
This is the same example as in the previous section, wrapped according to the catalog YAML requirements, with one new block added defining an enricher. An enricher creates a new sensor from other values; in this case it will create a main.uri
sensor by populating a printf
-style string "http://%s:%s"
with the sensor values.
With this added to the catalog, we can reference the type netcat-example
when we deploy an application. Return to the Home or Applications tab, click +, and submit this YAML blueprint:
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-reference.yaml %} {% endhighlight %}
This extends the previous blueprint which we registered in the catalog, meaning that we don‘t need to include it each time. Here, we’ve elected to supply our own message, but we'll use the default port. More importantly, we can package it for others to consume -- or take items others have built.
We can go further and use this to deploy a cluster, this time giving a custom port as well as a custom message:
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-cluster.yaml %} {% endhighlight %}
In either of the above examples, if you explore the tree in the Applications view and look at the Summary tab of any of the server instances, you‘ll now see the URL where netcat is running. But remember, netcat will stop after one run, so you’ll only be able to use each link once before you have to restart it. You can also run restart
on the cluster, and if you haven't yet experimented with resize
on the cluster you might want to do that.
One requirement of the launch script is that it store the process ID (PID) in the file pointed to by $PID_FILE
, hence the second line of the script. This is because Brooklyn wants to monitor the services under management. You'll observe this if you connect to one of the netcat services, as the process exits afterwards and Brooklyn sets the entity to an ON_FIRE
state. (You can also test this with a killall nc
before connecting or issueing a stop
command on the server -- but not on the example, as stopping an application root causes it to be removed altogether!)
There are other options for determining launch: you can set checkRunning.command
and stop.command
instead, as documented on the javadoc and config keys of the {% include java_link.html class_name=“VanillaSoftwareProcess” package_path=“org/apache/brooklyn/entity/software/base” project_subpath=“software/base” %} class, and those scripts will be used instead of checking and stopping the process whose PID is in $PID_FILE
.
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-more-commands.yaml %} {% endhighlight %}
And indeed, once you‘ve run one telnet
to the server, you’ll see that the service has gone “on fire” in Brooklyn -- because the nc
process stops after one run.
Besides detecting this failure, Brooklyn policies can be added to the YAML to take appropriate action. A simple recovery here might just to automatically restart the process:
{% highlight yaml %} {% readj example_yaml/vanilla-bash-netcat-restarter.yaml %} {% endhighlight %}
Autonomic management in Brooklyn often follows the principle that complex behaviours emerge from composing simple policies. The blueprint above uses one policy to triggering a failure sensor when the service is down, and another responds to such failures by restarting the service. This makes it easy to configure various aspects, such as to delay to see if the service itself recovers (which here we‘ve set to 15 seconds) or to bail out on multiple failures within a time window (which again we are not doing). Running with this blueprint, you’ll see that the service shows as on fire for 15s after a telnet
, before the policy restarts it.
For an even more interesting way to test it, look at the blueprint defining a netcat server and client. This uses initializers
to define an effector to sayHiNetcat
on the Simple Pinger
client, using env
variables to inject the netcat-server
location and parameters
to pass in per-effector data:
env: TARGET_HOSTNAME: $brooklyn:component("netcat-server").attributeWhenReady("host.name") brooklyn.initializers: - type: org.apache.brooklyn.core.effector.ssh.SshCommandEffector brooklyn.config: name: sayHiNetcat description: Echo a small hello string to the netcat entity command: | echo $message | nc $TARGET_HOSTNAME 4321 parameters: message: description: The string to pass to netcat defaultValue: hi netcat
This blueprint also uses initializers to define sensors on the netcat-server
entity so that the $message
we passed above gets logged and reported back:
launch.command: | echo hello | nc -l 4321 >> server-input & echo $! > $PID_FILE brooklyn.initializers: - type: org.apache.brooklyn.core.sensor.ssh.SshCommandSensor brooklyn.config: name: output.last period: 1s command: tail -1 server-input
These examples are relatively simple example, but they illustrate many of the building blocks used in real-world blueprints, and how they can often be easily described and combined in Brooklyn YAML blueprints. Next, if you need to drive off-piste, or you want to write tests against these blueprints, have a look at, for example, VanillaBashNetcatYamlTest.java
in the Brooklyn codebase, or follow the other references below.