= [wiki:GENIExperimenter/Tutorials/GENIExperimentEngine Get to Know the GENI Experiment Engine] = {{{ #!html
Hello GENI index Hello GENI index Hello GENI index
}}} = STEPS FOR EXECUTING EXERCISE = ---- '''Your goal in this tutorial is to fetch a parameterized URL on each node of your slicelet:''' '''!http://www.lively-web.org/nodejs/GEETutorial/helloWorld?slice=&name=&ip=&local=&lat=&lng=''' '''This page will log each of your queries, and you can check that all your nodes were successfully able to run the query.''' We will work up to this goal through hands-on learning with Ansible. ---- == 1. Experiment with various Ansible modules: ping, shell, setup == We will first get familiar with some basic Ansible tasks using the command-line interface. === (a) The ping module === The '''ping''' module simply tries to do a SSH login to a node and reports success or failure. Run the following command on your controller: {{{ $ ansible nodes -i ansible-hosts -m ping }}} If you don’t see success everywhere then there is something wrong with your setup. Ask one of the tutorial leaders for help. Note that you will be prompted to accept each node as you log into it; this happens only once per node, the first time you log in. === (b) The shell module === The '''shell''' module lets you run arbitrary SSH commands in parallel across a set of hosts. It’s useful for poking around, or if there is no Ansible module with the functionality you need. Try it out: {{{ $ ansible nodes -i ansible-hosts -m shell -a "hostname" }}} You can replace ''hostname'' above with any other Linux command. === (c) The setup module === The '''setup''' module gathers a bunch of information about each node and saves it in variables that you can reference in your Ansible playbooks. This will be really useful to do the tutorial! Try it out on a node to see what it collects (replace `` with your slicelet’s name): {{{ $ ansible .pcvm1-1.instageni.wisc.edu -i ansible-hosts -m setup }}} == 2. Create an Ansible playbook to download a parameterized URL from each node == === (a) Create a starter Ansible playbook === A playbook is a YAML file containing a list of Ansible tasks. To get started creating your Ansible playbook, copy the following into a file called lab.yaml: {{{ --- - hosts: nodes remote_user: root tasks: - name: An example of a debug statement debug: var=ansible_hostname }}} Run the playbook as: {{{ $ ansible-playbook -i ansible-hosts lab.yaml }}} The '''setup''' module is run automatically at the beginning of a playbook to populate variables for each node. The above playbook will dump the value of each node’s ''ansible_hostname'' variable. To run the playbook on a single node, replace ''nodes'' with the name of one of your slice nodes (e.g., slice338.pcvm3-7.instageni.nps.edu). Now, think about how you are going to solve the problems of this tutorial. You need to collect several pieces of information on each node: the container name, the IP of the host (i.e., the VM hosting the container), the IP of the container, and the latitude and longitude of the host. You then need to fetch a custom URL containing this information from each host. || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' Solve the problem on one node in your slice first, then deploy your solution to the remaining nodes. One thing at a time. || || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' Build your solution a piece at a time. Each step is, basically: (1) run a command, (2) possibly extract the information from the output and register it in an Ansible variable || || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' Starting an task in an Ansible playbook with "`- name:`", as in the example above, prints out the string following name at the beginning of the task. This is useful for keeping track of where you are in a playbook run. || === (b) Get the container name === Look at the variables collected by Ansible's setup module (step 1(c) above). Find one that holds the container name. Add a debug task to your playbook, like the one in the starter playbook, to print out its value. Complete the following task and add it to your playbook. {{{ - name: Print container name variable debug: var= }}} === (c) Get the container IP address === Look at the variables collected by Ansible's setup module (step 1(c) above). Find one that holds the container IP address. Add a debug task to your playbook, like the one in the starter playbook, to print out its value. Complete the following task and add it to your playbook {{{ - name: Print container IP address debug: var= }}} === (d) Get the host's public IP address === This is a bit trickier: how to get the host's IP address? The IP address visible inside the slicelet (as reported in the variable ''ansible_eth0.ipv4.address'') is a private address -- it is not the control address of the host. There are a number of ways that you could discover the control address, including running '''dig +short''' on the host’s name (see if you can find a variable that contains the host's name; HINT: you need it to SSH into the slicelet) or by running '''curl''' against a webserver that reports the client’s externally visible address. || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' The '''ansible''' command-line tool is a good way to try out Ansible tasks before putting them in your playbook. Look at the examples in part 1 above. || || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' Usually in an Ansible playbook you reference a variable by surrounding it in double curly brackets: ''{{ ansible_eth0.ipv4.address }}''. You can see examples of how variables are referenced in tasks in [https://github.com/ansible/ansible-examples/blob/master/language_features/get_url.yml this playbook]. || || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' When you run an Ansible command in a playbook, you can save the output into a new variable using '''register: varname''' Then you can retrieve the value later in the playbook using ''{{ varname }}'' or, for shell command output, ''{{ varname.stdout }}''. You can see an example of how to register a variable in [https://github.com/ansible/ansible-examples/blob/master/language_features/register_logic.yml this playbook]. || === (e) Get the latitude and longitude for each node === Another requirement of the lab is to map the host's control IP address obtained in the previous step to the latitude and longitude for each node. One way to do this is to use the '''geoiplookup''' tool, provided by package '''geoip-bin'''. {{{ $ geoiplookup -f }}} where '''' is the database of IP addresses and locations. You can find a good one at: http://geolite.maxmind.com/download/geoip/database/GeoLiteCity.dat.gz, which you’ll have to download to each node and unzip. A different approach would be to run '''curl''' against a webserver that maps IP address to latitude and longitude, such as http://ipinfo.io, and parse the output. '''NOTE:''' this particular website rate-limits the number of requests per node per day, so if you use it, ''make only a single request per node and save the result in a file''… keep in mind that everyone in the tutorial may be hitting this server from the same set of hosts! || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' The Ansible '''script''' module can be used to run arbitrary scripts in your slicelet. See: http://docs.ansible.com/script_module.html || || [[Image(wiki:GENIExperimenter/Tutorials/Graphics:tip.png, nolink, 50px, bottom)]] || '''Pro Tip:''' Not all the resources you may need are installed on the nodes! The '''apt''' Ansible module is useful for installing packages; see: http://docs.ansible.com/apt_module.html || At this point, you should have enough information to flesh out the base Ansible playbook. No need to hurry. Do each step, one at a time, and use the '''debug''' module to print out variable values after each step. This will help you get something working very quickly. == 3. Run the playbook == Once you have finished your playbook, run it against all the nodes! As a data point, our Ansible playbook contained six commands (not including debug commands) and used the '''apt''', '''shell''', and '''get_url''' modules. == 4. Verify that your playbook worked as expected == Once you have completed the tutorial, you can check where you’ve said hello from at: ''!http://www.lively-web.org/nodejs/GEETutorial/show_hellos?slice='' You should see an entry for each node in your slicelet. = [wiki:GENIExperimenter/Tutorials/GENIExperimentEngine/Finish Next: Teardown Experiment] =