CONTINUAL INTEGRATION – Page 52 – A Technical I.T./DevOps Blog

What is a White Box Computer?

Question
You have heard the term "white box computer." What is it?

Answer
A workstation or server that is not created by a well-recognized brand. Some people refer to plain flavors as "vanilla." If a data center is getting white-box servers, they are not getting Dell or HP servers. White-box servers are affordable and may compete with the public cloud. Commodity servers are well known for being acceptable for Hadoop.

See these sources for more information about white-box computers:

It is important to note that white box computers may have a bright future: "White boxes have shown they can hold their own in software-defined networking (SDN) deployments and supporting industry standards." (This quote was taken from Networkworld.com.)

White box computers should not be confused with white box testing. White box testing is also referred to as clear box testing (according to guru99.com). This testing involves seeing variables and the stages of transformation of the data -- as opposed to just looking at the output (as in blackbox testing where the process itself is not analyzed). White box testing is more complex than black box testing.

How Do You Troubleshoot the Terraform Error ‘unsupported argument aws_key_pair’?

Problem scenario
You run a terraform command. You get 'unsupported argument aws_key_pair'. You want terraform to create an EC-2 server with a specific key pair. What should you do?

Solution
Don't use "aws_key_pair", use "key_name". The aws_instance section in a .tf file uses a different keyword. (The aws_key_pair is for creating an key-pair in AWS.) Use the "key_name" field for aws_instances like this:

resource "aws_instance" "example" {
  ami           = "ami-01a1234abcd567"
  instance_type = "t2.micro"
  key_name      = "appleorange"
}

How is CI Different from CD?

Question
You have read that CI is different from CD. How are they different (CI vs. CD)?

Answer
CI, continual integration involves integrating code from two or more developers on a continual (regular or ongoing) basis. CD (with the "C" standing for continuous or continual) can refer to delivery (with a manual process into production) or deployment (an automatic process even to production)*.

Where Continuous Deployment focuses on the actual deployment, Continuous Delivery focuses on the release and release strategy.
https://harness.io/blog/continuous-delivery/continuous-delivery-vs-continuous-deployment/

However there may be no difference between continual delivery and continual deployment depending on the source**.

One source tends to say that CD subsumes CI.***

12 Factor App refers to separating the build and release stages. In keeping with 12 Factor App, Harness.io tends to say that the CI process involves producing an artifact whereas the CD process is the one that transfers that artifact. Thus the build stage may happen in CI and the release stage may happen with CD. We tend to think that in a world as complex as the one we live in, you can have CD without CI (with CI/CD and DevOps tools that are available with AWS and Azure). Thus we think CD does not necessarily subsume CI.

CI may have no environment; 12 factor app recommends that integration happen independent of an environment. CD is environment-dependent.

* https://stackify.com/continuous-delivery-vs-continuous-deployment-vs-continuous-integration/

** "It’s important to note that many credible authors do not differentiate between Continuous Delivery and Continuous Deployment." (This quote was taken from https://www.plutora.com/blog/continuous-integration-continuous-delivery-continuous-deployment.)

*** "The idea is to do CI, plus automatically prepare and track a release to production." (This quote was taken from https://semaphoreci.com/blog/2017/07/27/what-is-the-difference-between-continuous-integration-continuous-deployment-and-continuous-delivery.html.)

To learn more about CI, see this posting.

Are Zero Trust Networks More Secure than VPN-Protected Networks?

Question
Some companies are getting away from VPNs in favor of zero trust systems. It can help save money on bandwidth and facilitate a better network performance when every employee is working remotely. Are NoVPN Services More Secure for a Given Enterprise? Is it recommended to use non-VPN services?

Answer
We think this is a debatable whether VPNs (Virtual Private Networks) make systems more secure.

Some sources recommend getting rid of a VPN, such as TechRadar. The recommended way of implementing NoVPN (or zero trust) services would necessarily handle, by design, a compromised system not leading to more sequential compromises. The exposed web services all require authentication individually, and thus some people believe getting rid of a VPN is preferred from a security perspective.

Conversely, others opine that there are security advantages to NoVPN services. The book Security for Web Developers (published in late 2015) says that VPNs offer security advantages (page 59). CI servers (such as Jenkins) are designed to execute arbitrary code [to test the code itself]. These servers represent a significant potential vulnerability. Some modern sources recommend a VPN to help secure a CI server (e.g., page 313 of Terraform Up and Running). Clearly monitoring and reviewing of logs of the VPN can help you detect a security breach. VPNs can reduce an attack surface. From one pragmatic perspective, the prospect of checking the logs in one entry point (such as a VPN) is less daunting than checking the logs of multiple web service endpoints (such as those associated with a zero trust network). However from another pragmatic perspective, an enterprise may overestimate how secure their inner network is. Inside the perimeter, you may still want zero-trust services. The U.S. Government provided a sobering message in 2017: "…The Task Force notes that the cyber threat to U.S. critical infrastructure is outpacing efforts to reduce pervasive vulnerabilities," (taken from NIST 800-53, Revision 5 https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-53r5.pdf).

Here are sources that suggest there is such a thing as "best practices" for enterprise VPN implementations:

But the utilization of a VPN would tend to refute the preference that many businesses have for zero trust or NoVPN solutions.

Here are sources that suggest there is such a thing as "best practices" for zero trust implementations:

The DevOps Handbook suggests zero trust may be better than a VPN implementation because it says there is a myth in the I.T. industry that "[s]afety can be improved by more barriers and protection; more layers of protection results higher safety..." (page 360).

If you use Zero Trust, you will not use a VPN. The existence of best practices with each network security model suggests that there is a lack of consensus in the networking industry on the "best practice."

As an aside, all best practices are not practicable because they are sometimes incompatible. If you want to read about the controversy surrounding "best practices" versus "recommended practices" in I.T./software, see this posting.

How Do You Troubleshoot a CentOS Installation Message “Error setting up base repository”?

Problem scenario
You are installing CentOS 8.x but when you click on the "Installation Source" tab, nothing happens. You do not see an option to enter an installation source.

You cannot click "Begin installation." What do you do?

Solution
Try different installation media. If you are using a boot.iso, this problem may happen.
Some DVD isos are here: http://ftp.hosteurope.de/mirror/centos.org/8/isos/x86_64/

How Do You Eliminate Unintended Indentation in Code?

Problem scenario
You are using WordPress for you website. You have code that has an indentation of one to three spaces that you do not want. You did not intend for this indentation. It is usually just one line -- the top line.

Here is an example:

How can you eliminate this indentation of your code?

Solution
Root cause
If you have a new line in the paragraph, there can be unintended indentation even if there are no leading spaces; it seems like a bug that has gone on for years.

Procedures (or workaround)
Create a new block. If you highlight some text in a Paragraph block, and then go to "<> Inline code", this can cause unintentional indentation.

If you create a new block, then click the plus sign icon, you can go to "<> Code". Then put the code there.

What is the Difference between global and nonlocal in Python?

Question
It seems like "global" and "nonlocal" would be the same thing. How are these keywords different in Python?

Answer
Variables inside a function are local by default; variables outside of functions are global by default. (This was taken from https://www.programiz.com/python-programming/global-keyword.) This answer/article addresses the "LEGB lexical scoping rule" (taken from page 872 of Learning Python).

The "nonlocal" keyword has two requirements that "global" does not have: 1) "nonlocal" must be enclosed in a function within a function; the keyword "def" is crucial here. 2) the variable that the "nonlocal" keyword operates on must be assigned in an outer function (one subsuming the function where the "nonlocal" keyword is).

The "nonlocal" keyword only operates within the scope of the parent function that subsumes the nested/sub function. The "global" keyword will affect the variable at the module level (not inside of a function), but the "nonlocal" keyword will not affect variables outside of any function. "Modules are probably best understood as simply packages of names…" page 694 of Learning Python. In Python "…files morph into namespaces" (page 695 of Learning Python). A source code file with Python statements and Python syntax is a module. One Python program can use other .py files with an "import" command. Outside of any function's definition, you are said to be at the "module level" (but not when you are inside a function).

To clarify "[t]his means that the [nonlocal] variable can be neither in the local nor the global scope." (This was taken from a medium.com article.)

"Python's name-resolution scheme is sometimes called the LEGB rule, after the scope of names: … When you use an unqualified name inside a function, Python searches up to four scopes--the local (L) scope, then the local scopes of any enclosing (E) defs and lambdas, then the global (G) scope, and then the built-in (B) scope--and stops at the first place the name is found. If the name is not found during this search, Python reports an error." This was taken from page 488 from Learning Python.

Sorting Algorithm Quiz & Answers

1. What of the following requires the most memory space?

a. Quick Sort
b. Bubble Sort
c. Merge Sort
d. Insertion Sort
e. Selection Sort

Answer: C. Source: https://www.bigocheatsheet.com/#:~:text=Array%20Sorting%20Algorithms%20%20%20%20Algorithm%20,%20O%20%28n%29%20%2010%20more%20rows%20

2. What sorting algorithm is canonically the best for data sets that cannot reside in memory (and must be persisted to disk)?

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

Answer: E. Merge sort. Source page 149 of Programming Interviews Exposed.

3. Which sorting algorithm does this describe?

Without doing comparisons among the elements, iteratively placing elements into buckets those items based on the least significant digit, then placing them into sub-buckets based on the second least significant digit, until it reaches the most significant digit.

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

Answer: A
Source: https://www.geeksforgeeks.org/radix-sort/

4. Which sorting algorithm does this describe?

Take non-overlapping partitions of the data set, order them individually, then build a larger ordered partition from the smaller sub-portions until you have an ordered result.

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

Answer: E. Source: Pages 148 and 149 of Programming Interviews Exposed.

5. Which sorting algorithm does this describe?

Gradually build a sorted array by taking one random element at a time from the source array. Each new element is placed in order via comparison with sorted elements in what will be the final result.

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

Answer: C. Insertion sort.
Source: Page 145 of Programming Interviews Exposed.

6. Which sorting algorithm does this describe?

Take one element to be a pivot value. Place all bigger and equal elements to the left of the pivot value and all the smaller values to the right. To sort these smaller sub-partitions to the left and right, take one element to be a pivot value. Place all bigger or equal elements of this subpartition to the right of this pivot value and elements that are smaller to the left.

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

Answer: F. Quicksort. Source: Page 146 of Programming Interviews Exposed.

7. Which sorting algorithm does this describe?

Find the smallest element then move it to the far left. Find the second smallest element, then move it to the second-to-most-left position. Find the third smallest element…

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

Answer: D. Source: Page 144 of Programming Interviews Exposed.

8. In the I.T. industry it is common to code various sorting algorithms in the workplace.

True
False

Answer: False. Source page 143 of Programming Interviews Exposed.

9. A comparison-based sorting algorithm in a worst case scenario can have which of the following runtime complexities?

a. O(N)
b. O(n log n)
c. O(n^2)
d. None of the above

Answer: B. Source: Page 144 of Programming Interviews Exposed by Mongan, Kindler and Giguere.

10. What is the average runtime complexity of insertion sort?

a. O(n)
b. O(n log n)
c. O(n^2)
d. None of the above.

Answer: C. Source page 146 of Programming Interviews Exposed by Mongan, Kindler and Giguere.

Sorting Algorithm Quiz Published!

Click here to see the quiz.

Sorting Algorithms Quiz

1. What of the following requires the most memory space?

a. Quick Sort
b. Bubble Sort
c. Merge Sort
d. Insertion Sort
e. Selection Sort

2. What sorting algorithm is canonically the best for data sets that cannot reside in memory (and must be persisted to disk)?

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

3. Which sorting algorithm does this describe?

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

4. Which sorting algorithm does this describe?

Take non-overlapping partitions of the data set, order them individually, then build a larger ordered partition from the smaller sub-portions until you have an ordered result.

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

5. Which sorting algorithm does this describe?

Gradually build a sorted array by taking one random element at a time from the source array. Each new element is placed in order via comparison with sorted elements in what will be the final result.

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

6. Which sorting algorithm does this describe?

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

7. Which sorting algorithm does this describe?

Find the smallest element then move it to the far left. Find the second smallest element, then move it to the second-to-most-left position. Find the third smallest element…

a. Radix sort
b. Bubble sort
c. Insertion sort
d. Selection sort
e. Merge sort
f. Quick sort

8. In the I.T. industry it is common to code various sorting algorithms in the workplace.

True
False

9. A comparison-based sorting algorithm in a worst case scenario can have which of the following runtime complexities?

a. O(N)
b. O(n log n)
c. O(n^2)
d. None of the above

10. What is the average runtime complexity of insertion sort?

a. O(n)
b. O(n log n)
c. O(n^2)
d. None of the above.