Ingo Pfennigstorf

## Central Logging Service for Distributed Applications

With the release of our great new presentation layer for the [Goettingen
Digitization Centre](https://gdz.sub.uni-goettingen.de) we faced new
problems. The Application consists of many different separate services
(and servers). For example a Symfony frontend application, separate
applications to deliver and process IIIF manifests and images. One
service is responsible to get and process newly scanned works, one
genereates PDF files, and so on.

Each service may fail and behave somehow unexpected, but these errors
are not visible to the user, but logged inside the application.

Slowly we get to the point, but one may imagine, that looking for errors
in each of these services and handling with different logging formats is
a lot of work and very error prone.

So, using a central logging server for all these applications is the
solution to our problem. We decided to use
[Graylog2](https://www.graylog.org/) that is quite easy to setup in our
docker-based environment. It's nothing more than

::: {.language-plaintext .highlighter-rouge}
::: {.highlight}
``` highlight
docker run --name mongo -d mongo:3 docker run --name elasticsearch \ -e "http.host=0.0.0.0" -e "xpack.security.enabled=false" \ -d docker.elastic.co/elasticsearch/elasticsearch:5.6.6 docker run --link mongo --link elasticsearch \ -p 9000:9000 -p 8441:8441/udp -p 12201:12201 -p 514:514 -p 53160:53160/udp -p 7946:7946/udp -p 8084:8084 \ -e GRAYLOG_WEB_ENDPOINT_URI="https://logging.example.com:9000/api" \ -d graylog/graylog:2.4.3-1 
```
:::
:::

and the service is up.

Next up, we configure our Symfony Apps to use the Gelf LogHandler (the
default format for logging to Graylog2).

`composer require graylog2/gelf-php`{.language-plaintext
.highlighter-rouge} adds the formatter and adding a service and add the
handler to the monolog configuration like that:

In `services.yml`{.language-plaintext .highlighter-rouge}:

::: {.language-plaintext .highlighter-rouge}
::: {.highlight}
``` highlight
 monolog.gelf_handler: class: Monolog\Handler\GelfHandler arguments: ["@gelf.publisher", 200] gelf.validator: class: Gelf\MessageValidator gelf.transport: class: Gelf\Transport\TcpTransport arguments: ['%env(LOG_DOMAIN)%', '%env(LOG_PORT)%'] gelf.publisher: class: Gelf\Publisher arguments: ["@gelf.transport", "@gelf.validator"] 
```
:::
:::

and finally the monolog configuration in
`config.yml`{.language-plaintext .highlighter-rouge}:

::: {.language-plaintext .highlighter-rouge}
::: {.highlight}
``` highlight
monolog: handlers: main: type: fingers_crossed level: info handler: gelf gelf: type: service id: monolog.gelf_handler level: debug 
```
:::
:::

With these small steps we have a fully working, centralized logging for
our services (at least our Symfony applications).

![graylog](assets/images/graylog2.png)


Central Logging Service for Distributed Applications   With the release of our great new presentation layer for the Goettingen Digitization Centre we faced new problems. The Application consists of many different separate services (and servers). For example a Symfony frontend application, separate applications to deliver and process IIIF manifests and images.

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Logging for distributed applications