Check Command: check_http
=========================

Check the status of a HTTP/HTTPS server running on a domain or IP
address on a remote host.

The included default check_https command uses the IP address of your
host, as configured in NEMS Configurator.

check_http Argument Syntax
--------------------------

+------+---------------------+---------------------------------------------+
| `-H` | `-\\-hostname`      | host name of the server where HTTP (or      |
|      |                     | HTTPS) daemon is running                    |
+------+---------------------+---------------------------------------------+
| `-I` | `-\\-IP-address`    | ip address of the HTTP (or HTTPS) server    |
+------+---------------------+---------------------------------------------+
| `-p` | `-\\-port`          | Port number where HTTP server runs. Default |
|      |                     | is 80                                       |
+------+---------------------+---------------------------------------------+
| `-4` | `-\\-use-ipv4`      | This will use IPv4 connection               |
+------+---------------------+---------------------------------------------+
| `-6` | `-\\-use-ipv6`      | This will use IPv6 connection               |
+------+---------------------+---------------------------------------------+
| `-S` | `-\\-ssl` or        | This will use HTTPS using default 443 port  |
|      | `-\\-sni`           | Enable SSL/TLS hostname extension support   |
|      |                     | (SNI)                                       |
+------+---------------------+---------------------------------------------+
| `-C` | `-\\-certificate`   | Minimum number of days a SSL certiface must |
|      |                     | be valid.                                   |
+------+---------------------+---------------------------------------------+
| `-e` | `-\\-expect`        | Expected response string. Default is HTTP/1 |
+------+---------------------+---------------------------------------------+
| `-s` | `-\\-string`        | Expected content string.                    |
+------+---------------------+---------------------------------------------+
| `-u` | `-\\-url`           |  to check                                   |
+------+---------------------+---------------------------------------------+
| `-P` | `-\\-post`          |  encoded http POST data                     |
+------+---------------------+---------------------------------------------+
| `-N` | `-\\-no-body`       | Do not wait for whole document body to      |
|      |                     | download. Stop once the headers are         |
|      |                     | downloaded.                                 |
+------+---------------------+---------------------------------------------+
| `-M` | `-\\-max-age`       | Check whether a document is older than x    |
|      |                     | seconds. Use 5 for 5 seconds, 5m for 5      |
|      |                     | minutes, 5h for 5 hours, 5d for 5 days.     |
+------+---------------------+---------------------------------------------+
| `-T` | `-\\-content-type`  | Indicate content type in header for POST    |
|      |                     | request                                     |
+------+---------------------+---------------------------------------------+
| `-l` | `-\\-linespan`      | Regular expression can span to new line     |
|      |                     | (Use this with -r or -R option)             |
+------+---------------------+---------------------------------------------+
| `-r` | `-\\-regex` or      | Use this regular expression to search for   |
|      | `-\\-ereg`          | string in the HTTP page                     |
+------+---------------------+---------------------------------------------+
| `-R` | `-\\-eregi`         | Same as above, but with ignore case.        |
+------+---------------------+---------------------------------------------+
| `-a` | `-\\-authorization` | If the site uses basic authentication send  |
|      |                     | uid, pwd in the format uid:pwd              |
+------+---------------------+---------------------------------------------+
| `-A` | `-\\-useragent`     | Pass the specified string as “User Agent”   |
|      |                     | in HTTP header.                             |
+------+---------------------+---------------------------------------------+
| `-k` | `-\\-header`        | Add additional tags that should be sent in  |
|      |                     | the HTTP header.                            |
+------+---------------------+---------------------------------------------+
| `-L` | `-\\-link`          | The output is wrapped as  link              |
+------+---------------------+---------------------------------------------+
| `-f` | `-\\-onredirect`    | When a  is redirected, use this to either   |
|      |                     | follow the , or send ok, warning, or        |
|      |                     | critical notification                       |
+------+---------------------+---------------------------------------------+
| `-m` | `-\\-pagesize`      | Specify the minimum and maximum page size   |
|      |                     | expected in bytes. Format is                |
|      |                     | minimum:maximum                             |
+------+---------------------+---------------------------------------------+
| `-m` | `-\\-pagesize`      | Specify the minimum and maximum page size   |
|      |                     | expected in bytes. Format is                |
|      |                     | minimum:maximum                             |
+------+---------------------+---------------------------------------------+
| `-w` | `-\\-warning`       | Response time in seconds for warning state  |
+------+---------------------+---------------------------------------------+
| `-c` | `-\\-critical`      | Response time in seconds for critical state |
+------+---------------------+---------------------------------------------+
| `-t` | `-\\-timeout`       | Number of seconds to wait before connection |
|      |                     | times out. Default is 10 seconds            |
+------+---------------------+---------------------------------------------+

NEMS Configurator Service Parameter Examples
--------------------------------------------

Check if a host is responding on the default http port (ie., 80):

.. code-block:: console

   [blank]

Check if a host is responding on the default https port (ie., 443):

.. code-block:: console

   -S

Check if a host is responding on an alternate https port (ie., 8080):

.. code-block:: console

   -S -p 8080

Check the state of the hosts SSL certificate and treat as a problem if
it expires in 30 days or less:

.. code-block:: console

   -C 30

Troubleshooting
---------------

**I receive a message “CRITICAL - Cannot make SSL connection. SSL alert
number 40” when trying to check a secure web site**

Are you using Cloudflare or another SSL redirecting system where your
certificate might be shared with other hostnames? Try adding `-\\-sni` to
your service parameters to enable Server Name Indication (SNI), which
allows the server to safely host multiple TLS Certificates for multiple
sites, all under a single IP address.

Test openssl's response by running this command from your NEMS server:

.. code-block:: console

   openssl s_client -connect YOURDOMAIN.COM:443 -debug

**I receive a message “CRITICAL - Socket timeout after 10 seconds” on
NEMS TV Dashboard, Adagios and so-on**

This means the particular board you're using to run NEMS is a bit slow
for the task. By default, check_http will timeout after 10 seconds. But
what happens if your board takes 11? It generates the error “CRITICAL -
Socket timeout after 10 seconds”.

To remedy this, yes, you could move to a faster board. But I'd suggest
you could also add these two things to your service check ARGS as per
the syntax above:

-N - only download the headers: this will result in a smaller
transaction, which in turn takes less time.

-T 30 - increase the timeout to 30 seconds.

So your ARGS would become:

.. code-block:: console

   -N -T 30