Use memcached for caching URL mappings with xmemcached

ansible/roles/worker/files/systemd/system/memcached.service.d/override.conf

+[Service]
+ExecStart=
+# Leave off usage of the $LISTEN environment variable set by the distribution-
+# supplied memcached.service file, as it only binds to 127.0.0.1 and ::1 by
+# default.
+# Instead we use memcached's default binding by not supplying the "-l" option
+# which means we bind to INETADDR_ANY instead.
+ExecStart=/usr/bin/memcached -m ${CACHESIZE} -c ${MAXCONN} $OPTIONS

ansible/roles/worker/files/systemd/system/shortener.service

@@ -2,6 +2,7 @@
 Description=upbshrt.xyz backend
 
 [Service]
+Environment=MEMCACHED_CLIENTS="192.168.10.11:11211"
 ExecStart=/usr/bin/java -jar /opt/shortener/shortener.jar
 
 [Install]

ansible/worker.yml

@@ -25,6 +25,7 @@
             create: yes
             validate: 'visudo --check --file %s'
 
+    # TODO: Check if this is still needed
     - name: Add shortener user
       user:
         name: shortener
@@ -52,6 +53,24 @@
         state: started
         enabled: yes
 
+    - name: Install memcached
+      package:
+        name: memcached
+        state: present
+    - name: Create /etc/systemd/system/memcached.service.d/ directory
+      file:
+        path: /etc/systemd/system/memcached.service.d/
+        state: directory
+    - name: Copy override.conf override file to /etc/systemd/system/memcached.service.d/
+      template:
+        src: /vagrant/ansible/roles/worker/files/systemd/system/memcached.service.d/override.conf
+        dest: /etc/systemd/system/memcached.service.d/override.conf
+    - name: Start and enable memcached.service
+      systemd:
+        name: memcached
+        state: started
+        enabled: yes
+
     - name: Install OpenJDK 15
       package:
         name: jdk-openjdk

shortener/pom.xml

@@ -68,6 +68,12 @@
       <scope>runtime</scope>
     </dependency>
 
+    <dependency>
+      <groupId>com.googlecode.xmemcached</groupId>
+      <artifactId>xmemcached</artifactId>
+      <version>2.4.7</version>
+    </dependency>
+
     <!-- <editor-fold desc="Test dependencies" -->
     <dependency>
       <groupId>org.springframework.boot</groupId>

shortener/src/main/kotlin/xyz/upbshrt/shortener/ShortenerApplication.kt

 package xyz.upbshrt.shortener
 
+import net.rubyeye.xmemcached.MemcachedClient
+import net.rubyeye.xmemcached.XMemcachedClientBuilder
+import net.rubyeye.xmemcached.utils.AddrUtil
+
+import org.springframework.beans.factory.annotation.Value
 import org.springframework.boot.autoconfigure.SpringBootApplication
 import org.springframework.boot.runApplication
 import org.springframework.context.annotation.Bean
@@ -13,4 +18,8 @@ class ShortenerApplication {
 
     @Bean
     fun allowedUrlProtocols() = setOf("http", "https")
+
+    @Bean
+    fun memcachedClient(@Value("#{systemEnvironment['MEMCACHED_CLIENTS']}") memcachedClients: String): MemcachedClient =
+        XMemcachedClientBuilder(AddrUtil.getAddresses(memcachedClients)).build()
 }

shortener/src/main/kotlin/xyz/upbshrt/shortener/controller/UrlShorteningController.kt

@@ -5,10 +5,14 @@ import java.net.URLDecoder
 import java.net.URLEncoder
 import java.nio.charset.StandardCharsets
 import java.math.BigInteger
+import java.util.*
 
 import javax.validation.constraints.Pattern
 
+import net.rubyeye.xmemcached.MemcachedClient
+
 import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.beans.factory.annotation.Value
 import org.springframework.http.HttpStatus
 import org.springframework.http.MediaType
 import org.springframework.http.ResponseEntity
@@ -26,9 +30,19 @@ import xyz.upbshrt.shortener.repository.UrlMappingRepository
 
 @Validated
 @RestController
-class UrlShorteningController @Autowired constructor(private val repository: UrlMappingRepository,
+class UrlShorteningController @Autowired constructor(private val repository:          UrlMappingRepository,
+                                                     private val memcachedClient:     MemcachedClient,
                                                      private val allowedUrlProtocols: Set<String>) {
 
+    /**
+     * The expiration time for memcached entries inserted from this controller taken from the
+     * `MEMCACHED_EXPIRATION_TIME` environment variable.
+     *
+     * Defaults to an expiration time of three hours if that variable is unset.
+     */
+    @Value("#{systemEnvironment['MEMCACHED_EXPIRATION_TIME'] ?: 3 * 60 * 60}")
+    private var memcachedExpirationTime: Int? = null
+
     private fun handleMalformedId(id: String): Nothing =
         throw ResponseStatusException(HttpStatus.BAD_REQUEST, "'$id' is not a valid id for linking to a URL.")
 
@@ -88,6 +102,19 @@ class UrlShorteningController @Autowired constructor(private val repository: Url
 
         try {
             val urlMapping: UrlMapping = repository.save(UrlMapping(numericId, uri.toString()))
+
+            try {
+                /*
+                 * We use the decimal representation of the id as a key for the memcached entry to be consistent with
+                 * the database representation of UrlMapping which also stores the key as a regular integer.
+                 */
+                memcachedClient.set(
+                    urlMapping.id!!.toString(),
+                    memcachedExpirationTime!!,
+                    urlMapping.url
+                )
+            } catch (ignored: Exception) {}
+
             return ResponseEntity.ok(URLEncoder.encode(urlMapping.toString(), StandardCharsets.UTF_8))
         } catch (exception: NumberFormatException) {
             handleMalformedId(id!!)
@@ -112,16 +139,25 @@ class UrlShorteningController @Autowired constructor(private val repository: Url
             handleMalformedId(id)
         }
 
-        return repository
-            .findById(numericId)
-            .map {
-                ResponseEntity
-                    .status(HttpStatus.FOUND)
-                    .location(URI(it.url))
-                    .build<Nothing>()
-            }
-            .orElseThrow {
-                ResponseStatusException(HttpStatus.NOT_FOUND, "No mapped URL found for id '$numericId'.")
-            }
+        val targetUrl: Optional<String> = try {
+            /*
+             * Again use the base 10 representation instead of that of UrlMapping.ID_RADIX for consistency with the
+             * database.
+             */
+            memcachedClient.get(numericId.toString())
+        } catch (exception: Exception) {
+            repository
+                .findById(numericId)
+                .map { it.url }
+        }
+
+        return targetUrl.map {
+            ResponseEntity
+                .status(HttpStatus.FOUND)
+                .location(URI(it))
+                .build<Nothing>()
+        }.orElseThrow {
+            ResponseStatusException(HttpStatus.NOT_FOUND, "No mapped URL found for id '$id'.")
+        }
     }
 }

shortener/src/main/kotlin/xyz/upbshrt/shortener/entity/UrlMapping.kt

@@ -27,7 +27,7 @@ class UrlMapping(id: BigInteger?, url: String) {
             Parameter(name = SequenceStyleGenerator.INCREMENT_PARAM,   value = "1")
         ]
     )
-    private var id: BigInteger? = id
+    var id: BigInteger? = id
 
     @Column(length = 2048, nullable = false)
     var url: String = url