Find the current AMI image (i.e. Ubuntu 16.04) in AWS using command line

If you would like to programatically find the current image of a specific distribution in AWS for your region, with the use of the aws cli, use the following (in this example looking for Ubuntu 16.04).

This is from the examples in the documentation here: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/finding-an-ami.html

Getting detailed information about your Linux distribution

To be able to get a more detailed information about your current linux distribution, including the code names use the following:

Using strace for analyzing performance

There is a very nice example on the O’reilly ‘Linux Under The Hood’ training about using strace to compare performance of two commands that provide the same output but with different calls. The two different commands were: ls and echo *, that they both provide the listing of the current directory.

First using the strace with ls:

And using the same with echo *

So the difference in time is 0.00000 for the echo and 0.000601 for the ls.

Similarly the number of calls for the echo is 33, but ls is using 100.

HAProxy load balancing with ssl pass_through in front of Vault

Problem

You would like to set up HAProxy as the load balancer in your Vault cluster configuration. Vault is set up with internal storage (Raft), and you would also like to be able to pass the connection encrypted from the client to the Vault cluster member, without having HAProxy decrypt/encrypt the message.

Solution

Looking and searching around in the internet provides a few examples of how to do this. During this process there are different errors that you can see happening. There are certain things that you will need to do in order to debug and find the correct setup.

One of the main points is that HAProxy’s frontend and backend mode should be tcp instead of http.

Another thing that will help with debugging would be having access to both HAProxy’s and Vault (active) member logs.

Using curl with the -v flag is also very helpful.

One of the attempts of having HAProxy and Vault server communicate through HTTP/2 was resulting in the following errors:

on an external client (not HAProxy, or Vault).

the following on the HAProxy log:

and the following on the Vault log

Changing the configuration on HAProxy to use http1.1 solves the issue (/etc/haproxy/haproxy.cfg

Which results in the correct response now by using the HAProxy as a ssl pass_through load balancer.

SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch

Problem

Trying to configure and use an nginx server that uses intermediate certifcates, you get the error about values mismatch and nginx does not start

Solution

It seems that this is a common mistake and it is mentioned here: https://nginx.org/en/docs/http/configuring_https_servers.html. In order to fix this you will need to change/reverse the original order that you have concatenated the chain, as in:

Tail Vault auth logs

Problem

You would like to tail the Vault auth log files, but if you use the vault tag for auditing and your server is also named vault, you cannot filter out the vault auth logs only.

Solution

Use the client_login as the filter in grep: