A Technical I.T./DevOps Blog
Problem scenario
You run a kubectl command, but you get this problem: 'error: unable to recognize "foobar.yaml": no matches for kind "Deployment" in version "extensions/v1beta1"'
What should you do?
Solution
Change your yaml file so the apiVersion setting/value works. To learn more about the acceptable values, see this posting.
Problem scenario
You have a .txt file. You know Linux can support substitutions of strings with some type of expression. You want to use Bash to replace every occurrence in the file with a string. What should you do?
Solution
Let's assume the file you have is called coolfile.txt. Run these two commands to replace "foo" with "bar" every time "foo" is found in the file named coolfile.txt:
oldfile=$(cat coolfile.txt)
echo "${oldfile//'foo'/bar}" > newfile.txt
# The resulting file newfile.txt will have "bar" instead of "foo"Problem scenario
You want to quit a function, or return out of it, when a certain condition is met. How do you do this?
Solution
This program illustrates how it is done. You will want to run the program twice, once by leaving the "5" as it is, and a second time by changing the "5" to "6".
def cool(x):
if x == 5:
return "There was equivalence"
else:
y = x
print("This statement is printing as an illustration")
return "The comparison was NOT equivalent"
var1 = cool(5)
print(var1)Problem scenario
You compile a C program (with gcc foobar.cc) but you get an error message like this:
basicprog.c:5:13: warning: format '%d' expects argument of type 'int', but argument 2 has type 'char *' [-Wformat=]
printf ("y is a %d\n",y);
What do you do to not get this error?
Solution
While the code compiles, the executable may not run. A compilation error can be benign. For this case, string characters need a special syntax to be printed out.
Here is a line that will produce this error (with a variable named "y"):
printf ("y is a %d\n", y);
Here is a similar but corrected line that will be error free:
printf ("y is a %s\n",y);
The "%d" is appropriate for printing integer variables. For string variables, use "%s" syntax.
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Problem scenario
You want to use Terraform and Kubernetes (in EKS). How do you do this in a simple way to test it out?
Solution
Prerequisite
This assumes you have deployed EKS. If you need assistance, see this posting.
This assumes you have installed Terraform. If you need assistance, see this posting.
Procedures
git clone https://github.com/hashicorp/learn-terraform-provision-eks-cluster
cd learn-terraform-provision-eks-cluster/
terraform init
terraform plan # This command is optional
terraform apply
# It may take 20 minutes. This step "module.eks.aws_eks_cluster.this[0]: Still creating... " may take 15 minutes by itself. Be patient.terraform destroyProblem scenario
You run an AWS CLI command, but you get this error:
An error occurred (InvalidParameterException) when calling the CreateNodegroup operation: Following required service principals [eks.amazonaws.com] were not found in the trust relationships of clusterRole arn:aws:iam::12345678910:role/foobar
How do you fix this?
Solution
Draft a command like this (but replace "12345677810:role/foobar" with the equivalent string in the error, and replace foobar.amazonaws.com with the service principal in the error):
aws iam list-roles --query 'Roles[?Arn==arn:aws:iam::12345678910:role/foobar]' | grep foobar.amazonaws.comIf the above command returns nothing, try the command again without the "| grep foobar.amazonaws.com". If your Role was configured correctly, you may need to open a ticket with AWS Support. If nothing is returned from the command above with the "grep", you need to modify the role. Go to the AWS Management Console, go to IAM -> Roles. Click on the role, go to "Trust Relationships" and "Edit Trust Relationship." Modify it like this:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"Service": "foo.amazonaws.com"
},
"Action": "sts:AssumeRole"
},
{
"Effect": "Allow",
"Principal": {
"Service": "bar.amazonaws.com"
},
"Action": "sts:AssumeRole"
}
]
}Problem scenario
You want the dot utility to transform "terraform graph" command output to usable files. What should you do?
Solution
Run this command: sudo apt -y install graphviz
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Problem scenario
You want to test "mount -a" to verify your user has sufficient permissions. You cannot add a physical device to the Linux server. How do you confirm "mount" will work?
Solution
Create a directory to be a mount point:sudo mkdir /aaa
Find a block device to mount. One way would be to run this: sudo cat /proc/partitions
Once found, run this: sudo mount /dev/dm-2 /aaa
Run this command: sudo mount -l | grep aaa
Then the ouput will be something like this: /dev/mapper/foobar on /aaa type ext4 (rw, …)
Copy the /dev/mapper/foobar /aaa ext4 entries (all three). Back up the /etc/fstab file to /etc/fstab.bak
Update the /etc/fstab to have the three entries recently identified as the last line. For example, the last line will look something like this:/dev/mapper/foobar /aaa ext4
Unmount the newly mapped partition by using a command like this: sudo umount /dev/dem-2
Now run sudo mount -a
Run this command: sudo mount -l | grep aaa
Problem scenario
You are using Debian or Ubuntu Linux and you want to install PostgreSQL. What do you do?
Solution
Run these commands:sudo apt -y install postgresql
sudo systemctl start postgresql@11-main
sudo pg_ctlcluster 11 main start
