Horisontal skalering

Kør flere Ayakaleaf Pro-replikaer bag en load balancer med sticky sessions.

Én replika bruger én nodes CPU til hver kompilering: på vores testnoder med 2 vCPU’er tog seks samtidige kompileringer tre gange så lang tid som én, mens de andre noder stod ubrugte hen. Flere replikaer fordeler brugerne og deres kompileringer over noderne.

Dette følger Overleafs design for Horisontal skalering, oversat til Kubernetes:

Krav	Her
Delt MongoDB og Redis	10-mongo.yaml og 20-redis.yaml fra installationen
Delte hemmeligheder	Secret’en overleaf-secrets fra trin 2 har dem allerede
Projektfiler og historik i S3 (ikke NFS)	enhver S3-tjeneste, se S3; Garage dér som et eksempel i clusteret
En lokal disk pr. replika til kompileringer og uploads	hostPath /srv/overleaf-ha på hver node
Vedvarende routing, WebSockets, 10 min. timeouts, 50 MB uploads	HAProxy med Overleafs eksempelkonfiguration
git-bridge som singleton ved siden af én replika	git-bridge med overleaf-0 som søskende

Planlæg S3 fra starten. En instans, der allerede gemmer filer på sin volumen, kræver først S3-migreringen. Denne opsætning erstatter Deployment’en fra trin 5: slet den (kubectl delete -f 40-overleaf.yaml), før du anvender StatefulSet’et.

1. S3-lager

   Opsæt de tre buckets og to brugere som beskrevet i S3 med din S3-tjeneste eller med Garage i clusteret, og læg de fire nøgler i Secret’en overleaf-s3. Konfigurationen nedenfor bruger Garage-eksemplet fra den side.

2. Konfiguration

   Denne ConfigMap erstatter 30-config.yaml. Den tilføjer S3 og git-bridge og peger OVERLEAF_SITE_URL på load balanceren:

   60-config.yaml

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: overleaf-env
     namespace: overleaf
   data:
     OVERLEAF_APP_NAME: Ayakaleaf Pro
     OVERLEAF_SITE_URL: http://192.0.2.10:30081      # the load balancer (HAProxy) URL
     OVERLEAF_ADMIN_EMAIL: [e-mail]
     # Emails: add the sender and the SMTP server together, see Email delivery
     OVERLEAF_MONGO_URL: mongodb://mongo-0.mongo:27017,mongo-1.mongo:27017,mongo-2.mongo:27017/sharelatex?replicaSet=overleaf
     OVERLEAF_REDIS_HOST: redis
     REDIS_HOST: redis
     ENABLED_LINKED_FILE_TYPES: project_file,project_output_file,url
     ENABLE_CONVERSIONS: "true"
     EMAIL_CONFIRMATION_DISABLED: "true"
     OVERLEAF_TRUSTED_PROXY_IPS: loopback,10.244.0.0/16   # HAProxy runs in the pod CIDR
     # Sandboxed compiles, node paths: each replica owns /srv/overleaf-ha on its node
     SANDBOXED_COMPILES: "true"
     SANDBOXED_COMPILES_SIBLING_CONTAINERS: "true"
     DOCKER_RUNNER: "true"
     SANDBOXED_COMPILES_HOST_DIR_COMPILES: /srv/overleaf-ha/data/compiles
     SANDBOXED_COMPILES_HOST_DIR_OUTPUT: /srv/overleaf-ha/data/output
     SANDBOXED_COMPILES_HOST_DIR_CACHE: /srv/overleaf-ha/data/cache
     ALL_TEX_LIVE_DOCKER_IMAGES: ghcr.io/ayaka-notes/texlive-full:2026.1
     ALL_TEX_LIVE_DOCKER_IMAGE_NAMES: TeX Live 2026
     TEX_LIVE_DOCKER_IMAGE: ghcr.io/ayaka-notes/texlive-full:2026.1
     # S3 (required for more than one replica); keys are in the Secret overleaf-s3
     OVERLEAF_FILESTORE_BACKEND: s3
     OVERLEAF_FILESTORE_TEMPLATE_FILES_BUCKET_NAME: overleaf-template-files
     OVERLEAF_FILESTORE_S3_ENDPOINT: http://garage:3900
     OVERLEAF_FILESTORE_S3_PATH_STYLE: "true"
     OVERLEAF_FILESTORE_S3_REGION: garage
     OVERLEAF_HISTORY_BACKEND: s3
     OVERLEAF_HISTORY_PROJECT_BLOBS_BUCKET: overleaf-project-blobs
     OVERLEAF_HISTORY_CHUNKS_BUCKET: overleaf-chunks
     OVERLEAF_HISTORY_S3_ENDPOINT: http://garage:3900
     OVERLEAF_HISTORY_S3_PATH_STYLE: "true"
     OVERLEAF_HISTORY_S3_REGION: garage
     # Git integration: one git-bridge, its sibling is overleaf-0
     GIT_BRIDGE_ENABLED: "true"
     GIT_BRIDGE_HOST: 10.96.100.80      # the git-bridge Service's fixed ClusterIP, see 75-git-bridge.yaml
     GIT_BRIDGE_PORT: "8000"
   
3. Replikaer

   70-overleaf.yaml

   apiVersion: v1
   kind: Service
   metadata:
     name: overleaf-hl
     namespace: overleaf
   spec:
     clusterIP: None            # stable DNS per replica: overleaf-0.overleaf-hl, ...
     selector:
       app: overleaf-ha
     ports:
       - {name: http, port: 80}
       - {name: web, port: 3000}       # git-bridge API (sibling only)
       - {name: history, port: 3100}   # history-v1, used by git-bridge via V1_HISTORY_URL
   ---
   apiVersion: apps/v1
   kind: StatefulSet
   metadata:
     name: overleaf
     namespace: overleaf
   spec:
     serviceName: overleaf-hl
     replicas: 3
     # OrderedReady: overleaf-0 runs the migrations alone before the next replica starts
     podManagementPolicy: OrderedReady
     selector:
       matchLabels:
         app: overleaf-ha
     template:
       metadata:
         labels:
           app: overleaf-ha
       spec:
         terminationGracePeriodSeconds: 60
         # Keep the environment to the ConfigMap and Secrets: no REDIS_PORT=tcp://..., GIT_BRIDGE_PORT=tcp://...
         enableServiceLinks: false
         affinity:
           podAntiAffinity:            # one replica per node: each uses that node's Docker and disk
             requiredDuringSchedulingIgnoredDuringExecution:
               - labelSelector:
                   matchLabels:
                     app: overleaf-ha
                 topologyKey: kubernetes.io/hostname
         containers:
           - name: sharelatex
             image: ghcr.io/ayaka-notes/overleaf-pro:6.3.2
             env:
               - name: POD_NAME
                 valueFrom:
                   fieldRef:
                     fieldPath: metadata.name
               # Each replica hands out history URLs with its own stable name, so git-bridge can reach them
               - name: V1_HISTORY_URL
                 value: http://$(POD_NAME).overleaf-hl.overleaf.svc.cluster.local:3100/api
             envFrom:
               - configMapRef: {name: overleaf-env}
               - secretRef: {name: overleaf-secrets}
               - secretRef: {name: overleaf-s3}
             ports:
               - containerPort: 80
             readinessProbe:
               httpGet: {path: /status, port: 80}
               periodSeconds: 10
             resources:
               requests: {cpu: 500m, memory: 1536Mi}
               limits: {memory: 3Gi}
             volumeMounts:
               - {name: local, mountPath: /var/lib/overleaf}
               - {name: docker-sock, mountPath: /var/run/docker.sock}
         volumes:
           # Local disk for ephemeral files (compiles, output, uploads); the HOST_DIR_* paths are under it
           - name: local
             hostPath: {path: /srv/overleaf-ha, type: DirectoryOrCreate}
           - name: docker-sock
             hostPath: {path: /var/run/docker.sock, type: Socket}
   

   • StatefulSet, ikke Deployment. Hver replika får et stabilt navn (overleaf-0, overleaf-1, …), som load balancerens cookie og git-bridge henviser til, og OrderedReady starter først overleaf-0 alene, så kun én replika kører databasemigreringerne.
   • Én replika pr. node. Hver replika starter sine kompileringer via sin nodes Docker og gemmer dem i sin nodes /srv/overleaf-ha.
   • V1_HISTORY_URL pr. replika. Hver replika udleverer historiklinks med sit eget navn, så git-bridge kan nå dem.
4. git-bridge

   75-git-bridge.yaml

   apiVersion: v1
   kind: Service
   metadata:
     name: git-bridge
     namespace: overleaf
   spec:
     # Fixed ClusterIP (inside the service CIDR): the sharelatex image's nginx proxies /git/ with
     # `resolver 127.0.0.11` (Docker's DNS), which does not exist in Kubernetes, so GIT_BRIDGE_HOST is this IP
     clusterIP: 10.96.100.80
     selector:
       app: git-bridge
     ports:
       - {name: http, port: 8000}
   ---
   apiVersion: apps/v1
   kind: StatefulSet
   metadata:
     name: git-bridge
     namespace: overleaf
   spec:
     serviceName: git-bridge
     replicas: 1
     selector:
       matchLabels:
         app: git-bridge
     template:
       metadata:
         labels:
           app: git-bridge
       spec:
         # Service "git-bridge" would inject GIT_BRIDGE_PORT=tcp://..., which git-bridge reads as its port
         enableServiceLinks: false
         containers:
           - name: git-bridge
             image: ghcr.io/ayaka-notes/overleaf-pro/git-bridge:6.3.2   # same version as the sharelatex image
             command: ["/server-pro-start.sh"]
             securityContext:
               runAsUser: 0
             env:
               - {name: GIT_BRIDGE_API_BASE_URL, value: "http://overleaf-0.overleaf-hl.overleaf.svc.cluster.local:3000/api/v0/"}
               - {name: GIT_BRIDGE_OAUTH2_SERVER, value: "http://overleaf-0.overleaf-hl.overleaf.svc.cluster.local"}
               - {name: GIT_BRIDGE_POSTBACK_BASE_URL, value: "http://git-bridge.overleaf.svc.cluster.local:8000"}
               - {name: GIT_BRIDGE_ROOT_DIR, value: /data/git-bridge}
             ports:
               - containerPort: 8000
             resources:
               requests: {cpu: 100m, memory: 256Mi}
               limits: {memory: 768Mi}
             volumeMounts:
               - {name: data, mountPath: /data/git-bridge}
     volumeClaimTemplates:
       - metadata:
           name: data
         spec:
           accessModes: [ReadWriteOnce]
           resources:
             requests:
               storage: 5Gi
   

   Se Git-integration for, hvorfor GIT_BRIDGE_HOST er en fast IP-adresse.

5. Load balancer

   HAProxy-konfigurationen er Overleafs eksempel med fem ændringer: /project/<id>/mcp routes til overleaf-0 ligesom /git/ (se MCP-server), almindelig HTTP på port 8080 (imaget kører som en ikke-root-bruger, der ikke kan binde port 80 under containerd), servere findes via cluster-DNS (pod-IP’er ændres ved hver genstart), et DaemonSet, så hver node svarer, og balance leastconn i stedet for standarden roundrobin (se spørgsmål og svar nedenfor).

   80-haproxy.yaml

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: haproxy-config
     namespace: overleaf
   data:
     haproxy.cfg: |
       global
         log stdout format raw local0 info
   
       resolvers kubedns
         parse-resolv-conf
         hold valid 10s
   
       defaults
         mode                    http
         # New sessions go to the replica with the fewest open connections (editors keep a WebSocket open)
         balance                 leastconn
         option                  httpchk HEAD /status
         http-check              expect status 200
         default-server          check resolvers kubedns init-addr none
         log                     global
         option                  httplog
         # Reroute to a different backend if the sticky one is down
         option                  redispatch 1
         retries                 3
         # Sticky session for 24h of inactivity -- compile output is deleted after 24h
         cookie                  server-pro-ha insert maxidle 24h
         timeout queue           1m
         timeout connect         15s
         timeout client          1m
         # Allow slow compiles -- hard-coded limit in clsi is 10min
         timeout server          10m
         # Disconnect the editor after 23h
         timeout tunnel          23h
         # Lower than NGINX_KEEPALIVE_TIMEOUT (65s) in the sharelatex container
         timeout http-keep-alive 60s
   
       listen overleaf
         bind :8080
         option forwardfor
         # When TLS ends in front of HAProxy, also pass:  http-request set-header X-Forwarded-Proto https
         # git requests go to the git-bridge sibling
         use-server overleaf-0 if { path_beg /git/ }
         # MCP clients send no cookie: keep compile, log and PDF download on one replica
         use-server overleaf-0 if { path_reg ^/project/[0-9a-f]{24}/mcp(/|$) }
         http-response add-header X-Served-By %s
         stats enable
         stats uri /haproxy
         server overleaf-0 overleaf-0.overleaf-hl.overleaf.svc.cluster.local:80 cookie overleaf-0
         server overleaf-1 overleaf-1.overleaf-hl.overleaf.svc.cluster.local:80 cookie overleaf-1
         server overleaf-2 overleaf-2.overleaf-hl.overleaf.svc.cluster.local:80 cookie overleaf-2
   ---
   apiVersion: apps/v1
   # DaemonSet: one HAProxy per node, so the NodePort answers on every node with externalTrafficPolicy
   # Local. The cookie holds the replica name, so stickiness works whichever HAProxy a request hits.
   kind: DaemonSet
   metadata:
     name: haproxy
     namespace: overleaf
   spec:
     selector:
       matchLabels:
         app: haproxy
     template:
       metadata:
         labels:
           app: haproxy
         annotations:
           config-hash: "1"   # bump to restart after editing the ConfigMap
       spec:
         containers:
           - name: haproxy
             image: haproxy:lts-alpine
             ports:
               - containerPort: 8080
             resources:
               requests: {cpu: 50m, memory: 32Mi}
               limits: {memory: 256Mi}
             volumeMounts:
               - {name: config, mountPath: /usr/local/etc/haproxy}
         volumes:
           - name: config
             configMap:
               name: haproxy-config
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: haproxy
     namespace: overleaf
   spec:
     type: NodePort
     externalTrafficPolicy: Local    # keep the client IP (no SNAT); only nodes running HAProxy answer
     selector:
       app: haproxy
     ports:
       - {name: http, port: 80, targetPort: 8080, nodePort: 30081}
   

   kubectl delete -f 40-overleaf.yaml --ignore-not-found
   kubectl apply -f 60-config.yaml -f 70-overleaf.yaml -f 75-git-bridge.yaml -f 80-haproxy.yaml
   kubectl -n overleaf rollout status statefulset/overleaf --timeout=20m
   curl -sI http://192.0.2.10:30081/login | grep -i x-served-by
   

   externalTrafficPolicy: Local bevarer brugernes IP-adresser i X-Forwarded-For.

6. TLS

   Afslut HTTPS i HAProxy som beskrevet i TLS-proxy, og sæt derefter OVERLEAF_SITE_URL til https://-adressen og OVERLEAF_SECURE_COOKIE: "true" i 60-config.yaml.

​

Hvad du kan forvente

Vi testede tre replikaer på tre noder med hver 2 vCPU’er og 4 GB, med MongoDB, Redis, Garage, git-bridge og HAProxy på de samme noder:

• 12 brugere, der kompilerede et dokument på 600 sider samtidig: alle 12 kompilerede og hentede deres PDF, 4 brugere pr. replika; en runde tog 8 til 18 sekunder. Hver node beholdt mindst 1,3 GB ledig hukommelse.
• Hver bruger bliver på én replika (cookie server-pro-ha), herunder PDF-downloadet, der skal komme fra den replika, der kompilerede det. Det samme gælder over HTTPS, herunder editorens WebSocket.
• Når en replika stopper, får dens brugere fejl i omkring 15 til 20 sekunder, indtil HAProxy markerer den som nede; derefter flyttes de til en anden replika og forbliver logget ind, fordi sessioner ligger i Redis.

​

Spørgsmål og svar

Hvorfor balance leastconn?

Svar: Med Overleafs eksempel (roundrobin, én HAProxy pr. node) endte 12 nye brugere med at fordele sig med 8, 3 og 1 på de tre replikaer i vores test, og den travleste replika fik de langsomste brugere til at vente 29 sekunder. Med leastconn, der foretrækker replikaen med færrest åbne forbindelser (hver editor holder en WebSocket åben), gav den samme test 4, 4 og 4 og 18 sekunder. Stickiness er uændret: den kommer fra cookien.

Kan jeg bruge min ingress-controller i stedet for HAProxy?

Svar: Ja, hvis den router via en cookie til en stabil replika, understøtter WebSockets, tillader forespørgselstider på 10 minutter og uploads på 50 MB, holder sin keep-alive-timeout under 65 sekunder, sender X-Forwarded-For og X-Forwarded-Proto og sender /git/ og /project/<id>/mcp til overleaf-0. Route til replikaernes egne navne (overleaf-N.overleaf-hl), ikke til en Service, der fordeler hver forespørgsel.

Hvordan tilføjer jeg en fjerde replika?

Svar: Tilføj en node med Docker og TeX Live-imagesene, sæt replicas: 4 i 70-overleaf.yaml, og tilføj en linje server overleaf-3 ... til HAProxy-konfigurationen (og forøg config-hash, så HAProxy genstarter).