Github user sjcorbett commented on a diff in the pull request:
https://github.com/apache/incubator-brooklyn/pull/741#discussion_r34260578
--- Diff: docs/guide/dev/tips/troubleshooting-connectivity.md ---
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+---
+layout: website-normal
+title: Troubleshooting Server Connectivity Issues in the Cloud
+toc: /guide/toc.json
+---
+
+A common problem when setting up an application in the cloud is getting
the basic connectivity right - how
+do I get my service (e.g. a TCP host:port) publicly accessible over the
internet.
+
+This varies a lot - e.g. is the VM public or in a private network, is the
service only accessible through
+a load balancer, should the service be globally reachable or only to a
particular CIDR.
+
+This blog post gives some general tips for debugging connectivity issues,
which are applicable to a
+range of different service types. Choose those that are appropriate for
your use-case.
+
+## VM reachable
+If the VM is supposed to be accessible directly (e.g. from the public
internet, or if in a private network
+then from a jump host)...
+
+### ping
+Can you `ping` the VM from the machine you are trying to reach it from.
+
+However, ping is over ICMP. If the VM is unreachable, it could be that the
firewall forbids ICMP but still
+lets TCP traffic through).
+
+### telnet to TCP port
+You can check if a given TCP port is reachable and listening using `telnet
<host> <port>`, such as
+`telnet www.google.com 80`, which gives output like:
+
+```
+ Trying 31.55.163.219...
+ Connected to www.google.com.
+ Escape character is '^]'.
+```
+
+If this is very slow to respond, it can be caused by a firewall blocking
access. If it is fast, it could
+be that the server is just not listening on that port.
+
+### DNS and routing
+If using a hostname rather than IP, then is it resolving to a sensible IP?
+
+Is the route to the server sensible? (e.g. one can hit problems with proxy
servers in a corporate
+network, or ISPs returning a default result for unknown hosts).
+
+The following commands can be useful:
+
+* `host` is a DNS lookup utility. e.g. `host www.google.com`.
+* `dig` stands for âdomain information groperâ. e.g. `dig
www.google.com`.
--- End diff --
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