<h1 id="regular-tcpdump">Regular TCPDUMP</h1>
<p>Since tcpdump is installed by default, it's the first thing to use</p>
<pre><code class="language-bash"># Only listen on one interface
tcpdump -i &#x3C;interface/any>

# Filter to a host
tcpdump 'host &#x3C;ip address/fqdn>'

# filter to a port
tcpdump 'tcp port 5000'

# combine filters
tcpdump '(tcp port 5000 or tcp port 35357) and host 192.168.0.100'

# print packets in ascii (basically always want this)
tcpdump -A

</code></pre>
<h1 id="using-tshark">Using tshark</h1>
<p>Another option is wireshark's command line, tshark:</p>
<pre><code class="language-bash">apt-get install tshark
</code></pre>
<p>Note that tshark is really slow to get started compared to tcpdump, you need to wait a good while
until it says something like "Capturing on 'eno1'"</p>
<pre><code class="language-bash"># show interfaces
tshark -D

# Capture everything from a given source and interface
tshark -i eno1 -Y "ip.src == 10.1.0.76"

# Capture HTTP to and from a given source
tshark -i eno1 -Y "ip.addr == 10.1.0.76 and http"
</code></pre>


<p>This post covers getting started with a very simple Google Cloud Functions API,
a great serverless solution with affordable pricing. This API will pull the
IP address from the HTTP request, and return <code>Hello &#x3C;source IP></code>.</p>
<hr>
<h3 id="table-of-contents">Table of Contents</h3>
<ul>
<li><a href="#pricing-details">Pricing Details</a></li>
<li><a href="#deploy-hello-world-function">Deploy Hello World Function</a>
<ul>
<li><a href="#mainpy">main.py</a></li>
<li><a href="#requirementspy">requirements.py</a></li>
</ul>
</li>
<li><a href="#accessing-the-function">Accessing the Function</a>
<ul>
<li><a href="#from-the-console-web-ui">From the Console Web UI</a></li>
<li><a href="#from-the-request-url">From the Request URL</a></li>
</ul>
</li>
</ul>
<h1 id="pricing-details">Pricing Details</h1>
<p>Cloud Functions pricing is pretty affordable for most use cases, assuming you
write your functions in such a way that they don't get invoked a few too many
millions of times.</p>
<p>Check the official <a href="https://cloud.google.com/functions/pricing">Google docs</a>
for accurate and up-to-date pricing, but here's what it looked like at the time
of my writing this.</p>
<p>Pricing is broken into a few fees:</p>
<ul>
<li><em>Invocations</em>: A flat fee per function execution. $0.0000004 per invocation,
excluding the first 2 million.</li>
<li><em>Compute Time</em>: At the lowest clock speed (200MHz x 128MB RAM), compute costs
$0.000000231/100ms, ceil 100.</li>
<li><em>Networking</em>: $0.12/GB egress for data, while ingress is free.</li>
</ul>
<hr>
<h1 id="deploy-hello-world-function">Deploy Hello World Function</h1>
<p>Open <a href="https://console.cloud.google.com/functions/">Google Cloud Functions</a> in
your browser.</p>
<p>Create a function.</p>
<ul>
<li>Name: HelloWorld</li>
<li>Memory Allocated: 128 MB</li>
<li>Trigger: HTTP</li>
<li>Authentication: Allow unauthenticated invocations</li>
<li>Source code: Inline Editor</li>
<li>Runtime: Python 3.7</li>
<li>Other settings: Leave them as defaults</li>
</ul>
<h2 id="mainpy">main.py</h2>
<p>The API function defined by <code>Function to execute</code> accepts a
<a href="https://flask.palletsprojects.com/en/1.1.x/api/#incoming-request-data">flask.Request</a>
argument.</p>
<pre><code class="language-python">def hello_world(request):
    """" Return a Hello message to sender of the API call """
		return 'Hello {}!'.format(request.remote_addr)
</code></pre>
<h2 id="requirementspy">requirements.py</h2>
<p>You can leave this blank. It's a list of libraries that will be used.</p>
<hr>
<h1 id="accessing-the-function">Accessing the Function</h1>
<h2 id="from-the-console-web-ui">From the Console Web UI</h2>
<ol>
<li>Navigate to the <a href="https://console.cloud.google.com/functions">Functions page</a>.</li>
<li>Click on the 3 dots next to the function name, and choose "Test function".</li>
<li>Populate and JSON for the GET request in "Triggering event". The above
example doesn't accept any input data so <code>{}</code> is all you need.</li>
<li>Click "Test the function"</li>
</ol>
<h2 id="from-the-request-url">From the Request URL</h2>
<ol>
<li>Navigate to the <a href="https://console.cloud.google.com/functions">Functions page</a>.</li>
<li>Click the function's name to navigate to the "Function details" page</li>
<li>Go to the 'Trigger" tab</li>
<li>Find the URL. Copy it.</li>
</ol>
<p>You can now test the URL with curl, your browser, httpie, python, etc.</p>
<pre><code class="language-bash">https://&#x3C;region>-&#x3C;project>.cloudfunctions.net/HelloWorld
</code></pre>


Kyle Pericak

"It works in my environment"

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