app-httpd.conf

<VirtualHost *:8080>
    AllowEncodedSlashes NoDecode

    LoadModule proxy_module modules/mod_proxy.so
    LoadModule proxy_http_module modules/mod_proxy_http.so
    LoadModule proxy_wstunnel_module modules/mod_proxy_wstunnel.so
    LoadModule rewrite_module modules/mod_rewrite.so
    LoadModule include_module modules/mod_include.so
    LoadModule info_module modules/mod_info.so

    DocumentRoot /usr/local/apache2/htdocs/gridstudy/

    <Directory /usr/local/apache2/htdocs/gridstudy/>
        <Files "index.html">
          SetOutputFilter INCLUDES
        </Files>
        <FilesMatch "^(env\.json|idpSettings\.json)$">
          # FileETag Digest for stable Etags accross loadbalanced servers for mounted files.
          #   "FileETag Digest" is acceptable here because these are only small files so
          #   having to read the full content of the file instead of just the filesystem
          #   metadata is not prohibitedly expensive. A better alternative would be to find
          #   a way to have stable filesystem metadata on all servers because:
          #   - accessing file system metadata is a lot less expensive.
          #   - contrary to apache httpd, nginx doesn't have an option to change the ETag
          #     generation method and always uses the filesystem metadata (size, mtime),
          #     so using "FileEtag Digest" locks us in with apache httpd.
          #   NOTE: this doesn't apply to files in the image (their filesystem metadata
          #   is the same because it's from the image), only to mounted files (bind mount
          #   or volume mount in docker compose, configmap in kubernetes)
          #   NOTE2: Because we use single file bind mounts for our files, the contents
          #   and filesystem metadata of our files fall out of sync between the host and
          #   the containers when the file is deleted or replaced (more precisely, as
          #   soon as the inode number of the file changes) (this can happen quite silently
          #   if your editor replaces the file when saving), but this means using Digest doesn't
          #   solve this issue. This is a known docker limitation: https://github.com/moby/moby/issues/6011
          FileETag Digest
        </FilesMatch>
        Options +Includes
        Header set Cache-Control "no-cache"
    </Directory>

    <Directory /usr/local/apache2/htdocs/gridstudy/assets/>
        # All files in this folder are public and have in their name
        # the hash of their content, so cache them very aggressively
        # as per recommended best practices
        # NOTE: coincidentally, this moves us out of a nasty apache bug
        # where etags don't work at all with mod_deflate and apache never
        # sends 304 for its own etags (304 only when manually removing the
        # extra "-gzip" etag suffix). See
        # https://bz.apache.org/bugzilla/show_bug.cgi?id=45023
        Header set Cache-Control "public, max-age=31536000, immutable"
    </Directory>

    <Location "/actuator/info">
        SetHandler server-info
    </Location>
    AddModuleInfo mod_info.c 'Hostname: ${HOSTNAME}'

    # BEGIN Rewrite engine for SPA behavior and reverse proxy
    RewriteEngine On

    # helper definition to compute how many slashes we saw in the routed http request
    # which is then set with SSI to the html base in index.html. This allows
    # hosting the app at any path (e.g. not just at the root of a domain),
    # and from the same deployment config (no base url hardcoded in the deployment),
    # while still allowing the javascript client app routing to know which part of the path
    # to use for javascript routing, versus which path of the path is used for hosting routing.
    # Example:
    #   browser sends mydomain.com/myapp1/foo/bar/baz
    #   hosting routing strips mydomain.com/myapp1 and sends /foo/bar/baz to this server
    #   this server replies with <base="../.."> in index.html
    #   browser recovers the base using "../.." from the original url mydomain.com/myapp1/foo/bar/baz
    #     => hosting at mydomain.com/myapp1/
    #     => client route foo/bar/baz
    # The computed base is "." or ".." or "../.." or "../../.." and so on
    RewriteMap remapbase "prg:/bin/sed -u -e 's;[^ ]* ;;' -e 's;[ ?].*;;' -e 's;[^/]*;..;g' -e 's;../..;;' -e 's/.//' -e 's;^$;.;'"

    # For files (e.g. our css and javascript) or reverse proxied urls,
    # skip the classic SPA "rewrite everything to /index.html"
    RewriteCond /usr/local/apache2/htdocs/gridstudy%{REQUEST_URI} -f [OR]
    RewriteCond %{REQUEST_URI} ^/api/.* [OR]
    RewriteCond %{REQUEST_URI} ^/ws/.*
    RewriteRule ^ - [S=2]

    # We (ab)use a RewriteRule just to run the external computation of the base
    # and temporarily store the result in place of the request (it doesn't matter
    # as the request is always replaced with /index.html in the end anyway).
    # We must store it in place of the request because it will allow the next RewriteRule
    # to capture it and set it with the E flag in a variable for SSI to use
    RewriteRule ^ "${remapbase:%{THE_REQUEST}}" [DPI]

    # Note here for the slash in the pattern, it's because somewhere between
    # 2.4.55 and 2.4.68, rewrite_mod started to add a leading slash to our
    # computed base, as seen in the following logs
    #   mod_rewrite.c: rewrite '/' -> '.'
    #   mod_rewrite.c: add root prefix: . -> /.
    # so we capture everything except the the leading slash in the pattern
    # make it optional to hopefully improve resilience, this pattern must always
    # match to respond with the html for our SPA to work !
    RewriteRule "^/?(.*)$" /index.html [E=BASE:$1,L]

    # Needed if the request is directly index.html, the file exists and the rules are skipped
    # and base is not set so we set it here if unset
    SetEnvIf BASE ^$ BASE=.
    # END Rewrite engine for SPA behavior and reverse proxy

    ProxyRequests off
    ProxyPassMatch "^/api/gateway/(.*)$" http://gateway/$1 nocanon
    ProxyPassMatch "^/ws/gateway/(.*)$" ws://gateway/$1 nocanon

    LimitRequestLine 64000
</VirtualHost>