A daemon written in Clojure, designed and intended to be run as a microservice,
implementing a simple urban bus routing prototype
Rationale: This project is a direct Clojure port of the earlier developed urban bus routing prototype, written in Java using Spring Boot framework, and tailored to be run as a microservice in a Docker container. The following description of the underlying architecture and logics has been taken from here as is, without any modifications or adjustment.
Consider an IoT system that aimed at planning and forming a specific bus route for a hypothetical passenger. One crucial part of such system is a module, that is responsible for filtering bus routes between two arbitrary bus stops where a direct route is actually present and can be easily found. Imagine there is a fictional urban public transportation agency that provides a wide series of bus routes, which covered large city areas, such that they are consisting of many bus stop points in each route. Let's name this agency Trans-RoutE-Townish Co., Ltd. or in the Net representation — transroutownish.com, hence the name of the project.
A module that is developed here is dedicated to find out quickly, whether there is a direct route in a list of given bus routes between two specified bus stops. It should immediately report back to the IoT system with the result true if such a route is found, i.e. it exists in the bus routes list, or false otherwise, by outputting a simple JSON structure using the following format:
{
"from" : <starting_bus_stop_point>,
"to" : <ending_bus_stop_point>,
"direct" : true
}
<starting_bus_stop_point> and <ending_bus_stop_point> above are bus stop IDs: unique positive integers, taken right from inputs.
A bus routes list is a plain text file where each route has its own unique ID (positive integer) and a sequence of its bus stop IDs. Each route occupies only one line in this file, so that they are all representing something similar to a list — the list of routes. The first number in a route is always its own ID. Other consequent numbers after it are simply IDs of bus stops in this route, up to the end of line. All IDs in each route are separated by whitespace, usually by single spaces or tabs, but not newline.
There are some constraints:
- Routes are considered not to be a round trip journey, that is they are operated in the forward direction only.
- All IDs (of routes and bus stops) must be represented by positive integer values, in the range
1 .. 2,147,483,647. - Any bus stop ID may occure in the current route only once, but it might be presented in any other route too.
The list of routes is usually mentioned throughout the source code as a routes data store, and a sample routes data store can be found in the data/ directory of this repo.
Since the microservice architecture for building independent backend modules of a composite system are very prevalent nowadays, this seems to be natural for creating a microservice, which is containerized and run as a daemon, serving a continuous flow of HTTP requests.
This microservice is intended to be built locally and to be run like a conventional daemon in the VM environment, as well as a containerized service, managed by Docker.
One may consider this project has to be suitable for a wide variety of applied areas and may use this prototype as: (1) a template for building a similar microservice, (2) for evolving it to make something more universal, or (3) to simply explore it and take out some snippets and techniques from it for educational purposes, etc.
The microservice is known to be built and run successfully under Ubuntu Server (Ubuntu 22.04.3 LTS x86-64). Install the necessary dependencies (openjdk-17-jre-headless, clojure, leiningen, make, docker.io):
$ sudo apt-get update && \
sudo apt-get install openjdk-17-jre-headless clojure leiningen make docker.io -y
Build the microservice using Leiningen:
$ lein clean
$
$ lein compile :all
...
$ lein uberjar
...
Or build the microservice using GNU Make (it covers the same Leiningen build workflow under the hood, plus prepares the final all-in-one JAR file for further Docker containerization — this is preferred and encouraged build variant):
$ make clean
...
$ make # <== Compilation phase. (Be aware: classes produced might be overwritten by the jar target.)
...
$ make jar
...
$ make all # <== This is equivalent to the jar target.
...
Build a Docker image for the microservice:
$ # Pull the JRE image first, if not already there:
$ sudo docker pull azul/zulu-openjdk-alpine:17-jre-headless-latest
...
$ # Then build the microservice image:
$ sudo docker build -ttransroutownish/busclj .
...
Run the microservice using Leiningen (generally for development and debugging purposes):
$ lein run; echo $?
$ # ^ ^ ^
$ # | | |
$ # ------+---+---+
$ # Whilst this is not necessary, it's beneficial knowing the exit code.
...
Run the microservice using its all-in-one JAR file, built previously by the uberjar target:
$ java -jar target/uberjar/bus-0.20.3.jar; echo $?
...
Run a Docker image of the microservice, deleting all stopped containers prior to that:
$ sudo docker rm `sudo docker ps -aq`; \
export PORT=8765 && sudo docker run -dp${PORT}:${PORT} --name busclj transroutownish/busclj; echo $?
...
The following is not necessary but might be considered interesting — to look up into the running container, and check out that the microservice's all-in-one JAR file, log, and routes data store are at their expected places and in effect:
$ sudo docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
<container_id> transroutownish/busclj "java -jar bus.jar" About an hour ago Up About an hour 0.0.0.0:8765->8765/tcp, :::8765->8765/tcp busclj
$
$ sudo docker exec -it busclj sh; echo $?
/var/tmp $
/var/tmp $ java --version
openjdk 17.0.9 2023-10-17 LTS
OpenJDK Runtime Environment Zulu17.46+19-CA (build 17.0.9+8-LTS)
OpenJDK 64-Bit Server VM Zulu17.46+19-CA (build 17.0.9+8-LTS, mixed mode, sharing)
/var/tmp $
/var/tmp $ ls -al
total 8768
drwxrwxrwt 1 root root 4096 Nov 17 13:10 .
drwxr-xr-x 1 root root 4096 Sep 28 11:18 ..
-rw-r--r-- 1 root root 8957749 Nov 17 12:50 bus.jar
drwxr-xr-x 2 root root 4096 Nov 17 12:55 data
drwxr-xr-x 2 daemon daemon 4096 Nov 17 13:10 log
/var/tmp $
/var/tmp $ ls -al data/ log/
data/:
total 56
drwxr-xr-x 2 root root 4096 Nov 17 12:55 .
drwxrwxrwt 1 root root 4096 Nov 17 13:10 ..
-rw-r--r-- 1 root root 46218 Nov 17 12:40 routes.txt
log/:
total 12
drwxr-xr-x 2 daemon daemon 4096 Nov 17 13:10 .
drwxrwxrwt 1 root root 4096 Nov 17 13:10 ..
-rw-r--r-- 1 daemon daemon 59 Nov 17 13:10 bus.log
/var/tmp $
/var/tmp $ netstat -plunt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:8765 0.0.0.0:* LISTEN 1/java
/var/tmp $
/var/tmp $ ps ax
PID USER TIME COMMAND
1 daemon 0:03 java -jar bus.jar
41 daemon 0:00 sh
68 daemon 0:00 ps ax
/var/tmp $
/var/tmp $ exit # Or simply <Ctrl-D>.
0
All the routes are contained in a so-called routes data store. It is located in the data/ directory. The default filename for it is routes.txt, but it can be specified explicitly (if intended to use another one) in the resources/settings.edn file.
Identify, whether there is a direct route between two bus stops with IDs given in the HTTP GET request, searching for them against the underlying routes data store:
| HTTP request param | Sample value | Another sample value | Yet another sample value |
|---|---|---|---|
from |
4838 |
82 |
2147483647 |
to |
524987 |
35390 |
1 |
The direct route is found:
$ curl 'http://localhost:8765/route/direct?from=4838&to=524987'
{"direct":true,"from":4838,"to":524987}
The direct route is not found:
$ curl 'http://localhost:8765/route/direct?from=82&to=35390'
{"direct":false,"from":82,"to":35390}
The microservice has the ability to log messages to a logfile and to the Unix syslog facility. When running under Ubuntu Server (not in a Docker container), logs can be seen and analyzed in an ordinary fashion, by tailing the log/bus.log logfile:
$ tail -f log/bus.log
[2023-11-17][15:57:22][INFO ] Server started on port 8765
[2023-11-17][16:00:08][DEBUG] from = 4838 | to = 524987
[2023-11-17][16:00:08][DEBUG] 1 = 1 2 3 4 5 6 7 8 9 987 11 12 13 4987 415 ...
...
[2023-11-17][16:00:19][DEBUG] from = 82 | to = 35390
[2023-11-17][16:00:19][DEBUG] 1 = 1 2 3 4 5 6 7 8 9 987 11 12 13 4987 415 ...
...
[2023-11-17][16:05:10][INFO ] Server stopped
Messages registered by the Unix system logger can be seen and analyzed using the journalctl utility:
$ journalctl -f
...
Nov 17 15:57:22 <hostname> java[<pid>]: Server started on port 8765
Nov 17 16:00:08 <hostname> java[<pid>]: from = 4838 | to = 524987
Nov 17 16:00:19 <hostname> java[<pid>]: from = 82 | to = 35390
Nov 17 16:05:10 <hostname> java[<pid>]: Server stopped
Inside the running container logs might be queried also by tailing the log/bus.log logfile:
/var/tmp $ tail -f log/bus.log
[2023-11-17][13:10:21][INFO ] Server started on port 8765
[2023-11-17][13:17:25][DEBUG] from = 4838 | to = 524987
[2023-11-17][13:17:25][DEBUG] 1 = 1 2 3 4 5 6 7 8 9 987 11 12 13 4987 415 ...
...
[2023-11-17][13:17:32][DEBUG] from = 82 | to = 35390
[2023-11-17][13:17:32][DEBUG] 1 = 1 2 3 4 5 6 7 8 9 987 11 12 13 4987 415 ...
...
And of course Docker itself gives the possibility to read log messages by using the corresponding command for that:
$ sudo docker logs -f busclj
[2023-11-17][13:10:21][INFO ] Server started on port 8765
[2023-11-17][13:17:25][DEBUG] from = 4838 | to = 524987
[2023-11-17][13:17:25][DEBUG] 1 = 1 2 3 4 5 6 7 8 9 987 11 12 13 4987 415 ...
...
[2023-11-17][13:17:32][DEBUG] from = 82 | to = 35390
[2023-11-17][13:17:32][DEBUG] 1 = 1 2 3 4 5 6 7 8 9 987 11 12 13 4987 415 ...
...
When the query string passed in a request, contains inappropriate input, or the URI endpoint doesn't contain anything else at all after its path, the microservice will respond with the HTTP 400 Bad Request status code, including a specific response body in JSON representation, like the following:
$ curl 'http://localhost:8765/route/direct?from=qwerty4838&to=-i-.;--089asdf../nj524987'
{"error":"Request parameters must take positive integer values, in the range 1 .. 2,147,483,647. Please check your inputs."}
Or even simpler:
$ curl http://localhost:8765/route/direct
{"error":"Request parameters must take positive integer values, in the range 1 .. 2,147,483,647. Please check your inputs."}