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How to Create Temporary Files in Bash: mktemp and trap

How to Create Temporary Files in Bash: mktemp and trap mktemp command The generated temp file name is random and readable/writable only by the user. To ensure creation succeeds, append OR (||) after mktemp to exit on failure. To delete temp files on script exit, use trap to register cleanup. #!/bin/bash trap 'rm -f "$TMPFILE"' EXIT TMPFILE=$(mktemp) || exit 1 echo "Our temp file is $TMPFILE" mktemp options -d creates a temporary directory. -p specifies the directory for temp files. Default is $TMPDIR. If not set, /tmp is used. -t specifies a filename template. The template must end with at least three consecutive X characters for randomness; six X are recommended. The default template is tmp. followed by ten random characters. trap usage The trap command handles system signals in Bash scripts.

Monday, December 30, 2019 Read

Getting Started with GitHub Actions

Monday, December 23, 2019 Read

How Does Nginx Defend Against DDoS?

How Does Nginx Defend Against DDoS? Nginx limit module for access rate and max concurrent connections (DDoS protection) ngx_http_limit_req_module limit_req_zone $binary_remote_addr zone=mylimit:10m rate=10r/s;

Friday, December 20, 2019 Read

Golang Service Exceeded File Handle Limit (too many open files)

Golang Service Exceeded File Handle Limit (too many open files) Check system config: ulimit -a | grep open. The system config is normal. Check the service file limit: cat /proc/40636/limits. The service did not inherit the system settings and is still limited to 1024. Check open file count: lsof -p 40636 | wc -l. It exceeds the limit, so the error occurs. Check which connections are open: lsof -p 40636 > openfiles.log. Many HTTP connections were left open to the alerting service. The root cause is that the app failed to parse config, sent errors to the alerting service, and did not close connections, leading to too many open files. Why it did not inherit system limits needed more investigation.

Monday, December 16, 2019 Read

Trellis Ansible Bad Interpreter Error

Trellis Ansible Bad Interpreter Error Bad Interpreter Error Error we got using Ansible was a bad interpreter error. Python 2.7 is not to be found: zsh: /usr/local/bin/ansible-vault: bad interpreter: /usr/local/opt/python@2/bin/python2.7: no such file or directory And that was correct because when we checked /usr/local/opt we only had Python 3. Installation Python 2 brew install python@2 Python Crashing Hard Next, on Ansible version check I got another error ➜ trellis git:(master) ansible --version [1] 19153 abort ansible --version It was somehow crashing Python 2.7 though it should just work with it. I decided to upgrade Ansible as well

Friday, December 6, 2019 Read

Load Balancing with iptables and ip rule

Load Balancing with iptables and ip rule Steps This example uses an Arch Linux device with two Internet uplinks: eth0 and eth1. The mapping is: Mark 10 (0xa) - Routing table #110 - use eth0 Mark 11 (0xb) - Routing table #111 - use eth1 We decide which uplink to use based on the packet mark. First, use ip rule to map each mark to its routing table. The default routing table priority is 32768. To ensure our tables are used, set a higher priority (for example 31000).

Wednesday, December 4, 2019 Read

htop explained

Thursday, November 14, 2019 Read

Some Jenkinsfile examples

Some Jenkinsfile examples Parallel #!/usr/bin/env groovy pipeline { agent any stages { stage("Build") { steps { sh 'mvn -v' } } stage("Testing") { parallel { stage("Unit Tests") { agent { docker 'openjdk:7-jdk-alpine' } steps { sh 'java -version' } } stage("Functional Tests") { agent { docker 'openjdk:8-jdk-alpine' } steps { sh 'java -version' } } stage("Integration Tests") { steps { sh 'java -version' } } } } stage("Deploy") { steps { echo "Deploy!" } } } } When #!/usr/bin/env groovy pipeline { agent any environment { VALUE_ONE = '1' VALUE_TWO = '2' VALUE_THREE = '3' } stages { // skip a stage while creating the pipeline stage("A stage to be skipped") { when { expression { false } //skip this stage } steps { echo 'This step will never be run' } } // Execute when branch = 'master' stage("BASIC WHEN - Branch") { when { branch 'master' } steps { echo 'BASIC WHEN - Master Branch!' } } // Expression based when example with AND stage('WHEN EXPRESSION with AND') { when { expression { VALUE_ONE == '1' && VALUE_THREE == '3' } } steps { echo 'WHEN with AND expression works!' } } // Expression based when example stage('WHEN EXPRESSION with OR') { when { expression { VALUE_ONE == '1' || VALUE_THREE == '2' } } steps { echo 'WHEN with OR expression works!' } } // When - AllOf Example stage("AllOf") { when { allOf { environment name:'VALUE_ONE', value: '1' environment name:'VALUE_TWO', value: '2' } } steps { echo "AllOf Works!!" } } // When - Not AnyOf Example stage("Not AnyOf") { when { not { anyOf { branch "development" environment name:'VALUE_TWO', value: '4' } } } steps { echo "Not AnyOf - Works!" } } } }

Wednesday, November 6, 2019 Read

Jinja docx template, avoiding new line in nested for

Tuesday, October 29, 2019 Read

What the f*ck Python! 🐍

Friday, October 11, 2019 Read

Fighting ISP Cache Hijacking Again with iptables

Fighting ISP Cache Hijacking Again with iptables Cause The fight against the carrier cache problem started two years ago. The carrier even cached cnpm data. Worse, their cache servers were not only slow like a turtle in a marathon, they also crashed frequently, so I just wanted to write code but had to face a wall of red errors. Fix iptables -I FORWARD -p tcp -m tcp -m ttl --ttl-gt 20 -m ttl --ttl-lt 30 -j DROP

Monday, October 7, 2019 Read

Use Nginx and mod_pagespeed to Convert Images to WebP on the Fly

Use Nginx and mod_pagespeed to Convert Images to WebP on the Fly Compile ngx_pagespeed First make sure Nginx is built with --with-compat, so we do not need to rebuild Nginx from scratch. incubator: https://github.com/apache/incubator-pagespeed-ngx.git # Switch to the nginx source directory and configure the build ./configure --with-compat --add-dynamic-module=../incubator-pagespeed-ngx # Build modules make modules # Copy the built module into the nginx modules directory sudo cp objs/ngx_pagespeed.so /etc/nginx/modules/ # Create the cache directory for converted images sudo mkdir -p /var/ngx_pagespeed_cache sudo chown -R www-data:www-data /var/ngx_pagespeed_cache load_module modules/ngx_pagespeed.so; # enable pagespeed module on this server block pagespeed on; # Needs to exist and be writable by nginx. Use tmpfs for best performance. pagespeed FileCachePath /var/ngx_pagespeed_cache; # Ensure requests for pagespeed optimized resources go to the pagespeed handler # and no extraneous headers get set. location ~ "\.pagespeed\.([a-z]\.)?[a-z]{2}\.[^.]{10}\.[^.]+" { add_header "" ""; } location ~ "^/pagespeed_static/" { } location ~ "^/ngx_pagespeed_beacon$" { } pagespeed RewriteLevel CoreFilters; The last line (pagespeed RewriteLevel CoreFilters;) specifies the enabled optimizations. It includes basic filters such as:

Monday, October 7, 2019 Read