I started learning electronics a few days ago and I’m seeing resistors in every diagram I find and using them in pretty much all my experiments. So far, I’ve been using them blindly, but in this article I’m going to try to get a better understanding of what they actually do.

Electrical Resistance

A resistor is a component that implements electrical resistance. Electrical resistance is usually explained using a water and pipes analogy.

Let’s start by imagining two containers; One full of water and the other one completely empty:

This will be analogous to the two poles of a battery. One of them contains more electrons (water) than the other. While the two containers are not connected, water doesn’t flow.

Let’s now connect the two containers, but we’ll do it with an obstructed hose, so water can’t go through:

I’ve decided to try to learn electronics, and for this, I will of course need to interact with hardware (cables, resistors, diodes, etc…), but I’m lucky I was born in a time when a great deal of circuit design can be done from a computer using specialized software.

Being very new to this world and a stubborn Linux user, I did a quick search to try to find what’s my best option. I stumbled into this Electronics Circuit Simulator Software comparison page in Wikipedia.

I mainly looked at 3 things:

• Compatible with Linux
• Latest release date
• Open source

With these simple requirements, I found two contenders:

• Ngspice
• Qucs-S: Qucs with SPICE

Qucs-S has a nice graphical user interface, but depends on a SPICE back-end (e.g. Ngspice) to run. Due to this dependency, I’m going to be required to learn Ngspice anyway, so I decided to start with this one.

I’ve known about neovim for a long time, but I’ve never tried it out. My goal for this article is to try to replicate my current vim configuration:

• File explorer
• Grep
• Fuzzy file finder
• Syntax highlight
• .vimrc configuration

If Neovim is as good as people say, I should be able to do that, and it should run faster.

Installation

Neovim is already packaged for most OS. Sadly, the version included in Ubuntu is too old for most plugins out there. For this reason, we’ll have to build from source.

Install prerequisites:

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sudo apt-get install ninja-build gettext cmake unzip curl

When we create a java binary with bazel, we can run it using a command like this:

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bazel run :main

Sometimes an application requires very specific JVM flags to run correctly (For example: -Xmx:512m). These can be set like this:

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bazel run :main --jvmopt="-Xmx:512m" 

If we need to set more than one flag, we use this syntax:

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bazel run :main --jvmopt="-Xmx:512m" --jvmopt="-Xms:256m"

There are times that we want to figure out what command line options where used to start a java process. There are a few ways we can do this. The examples below assume PID is set to the process id we want to inspect:

ps

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ps -f $PID

UID          PID    PPID  C STIME TTY      STAT   TIME CMD
adrian    316721  313854  0 16:15 pts/6    Sl+    0:00 /home/adrian/.cache/bazel/_bazel_adrian/28381a26654a75034a8803698f5ef496/execroot/__main__/bazel-out/k8-fastbuild/bin/main.runfiles/local_jdk/bin/java -classpath main.jar -Xdebug example.Main

Using jps

jps doesn’t allow us to list a single process id, but we can see the command line arguments for all java processes:

We can use ps to get all the processes running in a host. The problem is that all java processes just say java by default. For example:

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ps -e | grep java

 309158 ?        00:00:16 java
 309527 ?        00:00:05 java
 313028 pts/3    00:00:00 java
 313346 ?        00:00:03 java

We can use the -f modifier to do full-format listing, which will print all the command line arguments used to start the process:

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ps -fe | grep java

adrian    309158   87625  0 15:03 ?        00:00:16 bazel(getting-pid-for-java-process) -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/home/adrian/.cache/bazel/_bazel_adrian/2cff94953bdedc4a1c6a41ce83e93da8 -Xverify:none -Djava.util.logging.config.file=/home/adrian/.cache/bazel/_bazel_adrian/2cff94953bdedc4a1c6a41ce83e93da8/javalog.properties -Dcom.google.devtools.build.lib.util.LogHandlerQuerier.class=com.google.devtools.build.lib.util.SimpleLogHandler$HandlerQuerier -XX:-MaxFDLimit -Djava.library.path=/usr/share/bazel/ -Dfile.encoding=ISO-8859-1 -jar /usr/share/bazel/A-server.jar --max_idle_secs=10800 --noshutdown_on_low_sys_mem --connect_timeout_secs=30 --output_user_root=/home/adrian/.cache/bazel/_bazel_adrian --install_base=/usr/share/bazel --install_md5=754af2f3778d588aa4604927527eee4e --output_base=/home/adrian/.cache/bazel/_bazel_adrian/2cff94953bdedc4a1c6a41ce83e93da8 --workspace_directory=/home/adrian/repos/ncona-code-samples/getting-pid-for-java-process --default_system_javabase=/usr/lib/jvm/java-11-openjdk-amd64 --failure_detail_out=/home/adrian/.cache/bazel/_bazel_adrian/2cff94953bdedc4a1c6a41ce83e93da8/failure_detail.rawproto --deep_execroot --expand_configs_in_place --idle_server_tasks --write_command_log --nowatchfs --nofatal_event_bus_exceptions --nowindows_enable_symlinks --client_debug=false --product_name=Bazel --noincompatible_enable_execution_transition --option_sources=install_Ubase:/etc/bazel/bazelrc:trust_Uinstall_Ubase:/etc/bazel/bazelrc
adrian    309527  309158  0 15:03 ?        00:00:05 /home/adrian/.cache/bazel/_bazel_adrian/2cff94953bdedc4a1c6a41ce83e93da8/execroot/__main__/external/local_jdk/bin/java -XX:+UseParallelOldGC -XX:-CompactStrings --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --patch-module=java.compiler=external/remote_java_tools_linux/java_tools/java_compiler.jar --patch-module=jdk.compiler=external/remote_java_tools_linux/java_tools/jdk_compiler.jar --add-opens=java.base/java.nio=ALL-UNNAMED --add-opens=java.base/java.lang=ALL-UNNAMED -jar external/remote_java_tools_linux/java_tools/JavaBuilder_deploy.jar --persistent_worker
adrian    313028  311741  0 15:35 pts/3    00:00:00 /home/adrian/.cache/bazel/_bazel_adrian/2cff94953bdedc4a1c6a41ce83e93da8/execroot/__main__/bazel-out/k8-fastbuild/bin/main.runfiles/local_jdk/bin/java -classpath main.jar example.Main
adrian    313346  309158  5 15:35 ?        00:00:02 /home/adrian/.cache/bazel/_bazel_adrian/2cff94953bdedc4a1c6a41ce83e93da8/execroot/__main__/external/local_jdk/bin/java -XX:+UseParallelOldGC -XX:-CompactStrings --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --patch-module=java.compiler=external/remote_java_tools_linux/java_tools/java_compiler.jar --patch-module=jdk.compiler=external/remote_java_tools_linux/java_tools/jdk_compiler.jar --add-opens=java.base/java.nio=ALL-UNNAMED --add-opens=java.base/java.lang=ALL-UNNAMED -jar external/remote_java_tools_linux/java_tools/JavaBuilder_deploy.jar --persistent_worker
adrian    313431  312937  0 15:36 pts/8    00:00:00 grep --color=auto java

This is better, but there is a lot of information so it is a little hard to find the process we are looking for.

Kafka is advertised as a distributed event store and stream processing platform. It’s used in many companies to reliably pass information between diferent systems in ways that traditional databases were not designed to do.

Let’s start by understanding why Kafka is called an event store.

In traditional databases (MySQL, for example) we can store records inside tables. Running these queries:

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INSERT INTO people(id, name) VALUES(111, "Carlos");
INSERT INTO people(id, name) VALUES(222, "Mario");
INSERT INTO people(id, name) VALUES(333, "Jose");

Gives us something like this:

You might be interested in these articles:

• Kubernetes networking with Istio
• Introduction to Jaeger Tracing

Envoy Tracing

In an Istio cluster, all applications are deployed with an Envoy proxy attached to them and Envoy supports integration with different tracing systems, this means, we can use Envoy’s features to automate tracing in our cluster.

This is what envoy can do for us:

• Initiate a trace when a request is received
• Propagate the trace-id over the cluster so spans can be connected
• Send information to tracing services like Jaeger

In this post we are going to learn how to generate a GPG key without having to answer prompts so it can be added to a script if desired.

We start by creating a file where we’ll write the details for our key. This will be the content of the file:

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%echo Generating GPG key
Key-Type: default
Key-Type: RSA
Key-Length: 3072
Subkey-Type: RSA
Subkey-Length: 3072
Name-Real: Carlos Sanchez
Name-Email: [email protected]
%no-protection
%commit
%echo done

And then we can use this command to generate the key:

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gpg --batch --gen-key <file path>

We can find all the options for generating the key in unattended key generation documentation.

Jaeger is an Open Source tracing framework written in Golang. Jaeger is compatible with OpenTracing which is an open source standard that specifies how tracing data should be formed.

Tracing

Tracing is concept that became popular with the rise of microservices (Service Oriented Architecture). When we work with microservices, the number of requests going through our internal network increases very quickly. To do its job a service might have to call a lot of services and some of those services might need to call other services.

When we make so many network requests it’s sometimes hard to understand where a failure is coming from. Tracing keeps track of the dependencies between different services and allows us to visualize it in a easy to understand manner.