cloud engineer
Here’s how to add a new route in Google Cloud Platform.
gcloud compute routes create name-of-new-route \ --destination-range=200.20.0.0/15 \ --next-hop-gateway=default-internet-gateway \ --project=host-project \ --network="default" \ --priority=900 |
When changing machine types, you may be asked to enable the latest ENA driver for Enhanced Network Support on an Amazon EC2 instance. There are several instructions depending on the Linux OS flavor. Here are the instructions to enable. In some cases, you may need to rebuild the kernel module. To verify that the ena module is installed, use the modinfo command as shown in the following example.
modinfo ena |
You also may have to enable the enhanced networking attribute on the instance.
aws ec2 modify-instance-attribute --instance-id instance_id --ena-support |
Here’s how to list all the devices on your network using nmap.
nmap -sn 192.168.0.0/24 |
If nmap is not installed, install it.
yum install nmap apt install nmap |
Netstat is a utility for gathering network statistics. It comes preinstalled on most systems.
If missing, here’s how to install.
# Redhat, CentOS yum install net-tools # Debian, Ubuntu, Mint apt install net-tools # SLES, SUSE zypper install net-tools |
Here are some common and useful commands.
# show version netstat -v # show routing table netstat -nr # show network interface statistics netstat -ai # show network connections netstat -ant # show network services netstat -pnltu |
I ran into an issue with Google Compute Engine TCP internal load balancer. The targets are unhealthy although all configs were correct installed. At one time the targets were working, but somehow they became unhealthy. In the end, 3 things needed to be checked.
You will need to change the server’s IP from DHCP to static to add ILB VIP.
SCP is similar to the CP or copy command, but it’s done via a secure network.
Here’s a CP command.
cp /dir1/filename /dir2 |
You can use SCP to copy file to another system. It requires login.
scp /dir1/filename user@server:/home/user |
This is using SCP to copy a file from 2 remote systems.
scp user@host1:/home/user/dir1/file.txt user@host2:/home/user/dir2 |
Here’s how to setup a Network Load Balancer in GCP.
Setup your instances.
# Instance 1 gcloud compute instances create www1 \ --image-family debian-9 \ --image-project debian-cloud \ --zone us-central1-b \ --tags network-lb-tag \ --metadata startup-script="#! /bin/bash sudo apt-get update sudo apt-get install apache2 -y sudo service apache2 restart echo '<!doctype html><html><body><h1>www1</h1></body></html>' | tee /var/www/html/index.html EOF" # Instance 2 gcloud compute instances create www2 \ --image-family debian-9 \ --image-project debian-cloud \ --zone us-central1-b \ --tags network-lb-tag \ --metadata startup-script="#! /bin/bash sudo apt-get update sudo apt-get install apache2 -y sudo service apache2 restart echo '<!doctype html><html><body><h1>www2</h1></body></html>' | tee /var/www/html/index.html EOF" # Instance 3 gcloud compute instances create www3 \ --image-family debian-9 \ --image-project debian-cloud \ --zone us-central1-b \ --tags network-lb-tag \ --metadata startup-script="#! /bin/bash sudo apt-get update sudo apt-get install apache2 -y sudo service apache2 restart echo '<!doctype html><html><body><h1>www3</h1></body></html>' | tee /var/www/html/index.html EOF" |
Create a firewall to allow external traffic to reach port 80.
gcloud compute firewall-rules create www-firewall-network-lb \
--target-tags network-lb-tag --allow tcp:80 |
Configure your network load balancer.
# Create an external IP address. gcloud compute addresses create network-lb-ip-1 \ --region us-central1 # Add a legacy HTTP health check. gcloud compute http-health-checks create basic-check # Add a target pool. gcloud compute target-pools add-instances www-pool \ --instances www1,www2,www3 \ --instances-zone us-central1-b # Add a forwarding rule. gcloud compute forwarding-rules create www-rule \ --region us-central1 \ --ports 80 \ --address network-lb-ip-1 \ --target-pool www-pool # Lookup external IP address. gcloud compute forwarding-rules describe www-rule \ --region us-central1 |
Finally, use the curl command to send traffic to the NLB external IP address.
while true; do curl -m1 [IP_ADDRESS]; done |
Tcpdump is a command line utility that allows you to capture and analyze network traffic going through your system. It is often used to help troubleshoot network issues.
# Find out if tcpdump is installed $ which tcpdump /usr/sbin/tcpdump # Install tcpdump sudo yum install -y tcpdump # Find which interface is available to you tcpdump -D # Capture on eth0. Use Ctrl-C to end capture. tcpdump -i eth0 # Capture after 10 packets tcpdump -i eth0 -c10 # Filter by port tcpdump -i any -c10 -nn port 80 # Filter by ip address tcpdump -i any -c10 -nn host 192.168.1.23 # Filter by source or destination ip tcpdump -i any -c10 -nn src 192.168.1.23 tcpdump -i any -c10 -nn dst 192.168.1.23 # Filter by destination ip and port tcpdump -i any -c5 -nn src 192.168.1.23 and port 80 # Save output to a file (binary format) tcpdump -i any -c10 -nn -w http.pcap port 80 # Save output to a file (text format) tcpdump -nn -r http.pcap |
Here’s a good intro article about tcpdump.
MTU means maximum transmission unit. The default value is 1500 for Ethernet, which is also the standard for the Internet. If your application or network requires a different MTU size, you can set the MTU size by running the following commands.
# Edit ifcfg-eth0 vi /etc/sysconfig/network-scripts/ifcfg-eth0 #Add MTU, settings: MTU="1460" # Save and close the file. Restart networking: service network restart |
Here are the steps how to migrate a GCP VM from one network to another. It involves recreating the instance in that network.