Exploring Logging in Caddy

Why Default Logs Are Not Enough? ## Understanding Caddy Logging Model ## Enabling JSON Access Logs ## Logging in a Docker-Based Load Balancer ## Which Upstream Handled This Request? ## Simulating Failure (Error Logs) ## Customizing Log Output ## Console Logs ## Choosing the Right Format ## Shaping Logs Without Changing Their Meaning ## Reducing Noise and Risk in Logs ## Reducing Noise by Removing Fields ## Obscuring Sensitive Information At some point, I realized that ‘it works’ is not enough. I need to know how it works too.” When something slows down or fails, the question is no longer “is the service running?” but: - Which component handled this request? - How long did it take? - Did the proxy retry or switch upstreams? Without clear answers, even a simple issue can turn into a long time debugging😆. This is where logging stops being a checkbox feature and starts becoming a core part of system design. By default, Caddy already gives you access logs. They show incoming requests, response status codes, and basic metadata. For simple setups, that might be sufficient. But once a system grows even slightly those logs start to fall short. The first issue is noise. Default logs tend to mix everything together: health checks, internal probes, real user traffic. Important signals get buried under routine requests. The second issue is missing context. When a request goes through a reverse proxy with load balancing, the most interesting part is often not the request itself, but what happens behind the scenes: - How long did the upstream take to respond? - Was there a retry or a fallback? Without this information, debugging becomes guesswork. A 502 response tells you that something failed, but not where or why. This post explores how to make Caddy logs actually useful especially in a Dockerized setup with reverse proxying and load-balanced Go APIs. Like most web servers, Caddy separates access logs from error logs. Access logs tell you what happened to a request. Error logs tell you why something went wrong. Access logs describe the lifecycle of an incoming request: - who made the request - how the server responded This is where most operational insights come from. When properly configured, access logs can tell you: - which upstream handled a request - how traffic is distributed - where latency is introduced Error logs focus on failures and exceptional cases: - upstream connection errors - TLS or protocol issues These logs are usually quieter, but they become critical when things break. They complement access logs by explaining why a request failed, not just that it failed. For this setup, I’m using a simple Go application as the backend worker. Each instance responds with its hostname, making it easy to see how requests are distributed by the load balancer. The full load-balancing setup, Caddy in front of three Go workers running in Docker has already been covered in a previous post. If you need the full context, you can refer to here: https://danielcristho.site/blog/go-caddy-load-balancer#the-project-setup When running Caddy inside Docker, the most practical logging strategy is to write logs to stdout and let Docker handle log collection. When you first run the stack: You’ll mostly see logs like: These are startup and internal runtime logs, not HTTP access logs. Access logs only appear after real HTTP traffic flows through Caddy. To make access logs enable JSON logging globally in the Caddyfile you can put output stdout like this. - logs are emitted to stdout - Docker captures them automatically Once the stack is running, send a few requests: You should see responses like: Now check the logs again: To make the logs more readable you can use jq: Using Debug Logs to Expose Load Balancer Decisions Earlier, we saw that standard access logs don’t explicitly show which backend handled a request. Caddy can expose upstream selection details, just not in access logs. The information lives in debug-level logs, specifically inside the reverse proxy handler. By enabling debug mode, Caddy reveals how routing decisions are made internally. In this mode, a single request produces logs like this, you can see which upstream that handled request "dial":"worker_3:8081": So far, everything looks fine. Requests succees and access logs show no anomalies. Real systems rarely fail all at once. They fail partially one backend goes down, a health check starts failing, or a connection becomes unstable. In this setup, stopping one worker is enough: Try to hit the URL again: From the client’s perspective, nothing breaks. Requests are still served, and responses keep coming back from the remaining healthy workers. This is exactly what we expect from a load balancer. Now if you see the logs again, there is an unhealthy upstream: This message is emitted by Caddy’s active health checker. It indicates that: - worker_2 is no longer reachable - the failure happens during health check probes Up to this point, all examples use JSON access logs. They are structured, machine-friendly, and easy to filter. Caddy allows you to control how logs are encoded, not just what gets logged. This is useful when the goal shifts from processing logs to reading them. Besides json, Caddy also provides a console encoder. It formats logs in a more friendly way while still preserving structure. After restarting the container, access logs will look like this: There is no universally “correct” log format. - JSON works best when logs are consumed by tools or pipelines. - Console works better when you are actively watching logs and debugging in real time. Caddy also allows fine-grained control over how log fields are named and formatted. This is not about adding new information, but about making existing information easier to work with. For example, you can: - rename common fields - control timestamp formats - standardize duration units - normalize log levels Here’s the updated access log after applying the custom JSON format: The structure of the log is still JSON, but key fields are now normalized: - level is uppercase (INFO) - readable timestamps and localized - duration is expressed in milliseconds instead of fractional seconds This makes the log easier to read during debugging. Once logs are readable and structured, the next concern is volume and exposure. Not every field in an access log is equally useful, and some of them are better left out entirely. Caddy allows selective filtering at the log level, making it possible to reduce noise without changing how requests are handled. Access logs often include fields that are technically correct but not relevant, like request headers. If headers are not part of your debugging workflow, you can remove them: With the request field removed entirely, access logs become significantly smaller: In other cases, it’s enough to remove only specific nested fields: Instead of deleting the entire request, selectively removing fields gives a better balance. Some fields should not be stored in plain text at all. Rather than relying on downstream redaction, Caddy can obscure sensitive data at the source: With IP masking enabled, the change is subtle but important: The request remains traceable across logs, but the exact client address is no longer exposed. Filtering is not about producing minimal logs. It’s about producing intentional logs. I only apply filters after understanding: - which fields I actually use - which ones are never read - Enabling logs is easy. Making them useful takes effort. - Access logs show what happened to a request. - Debug logs show how requests are routed. - Error logs show what fails behind the scenes. - Filtering and formatting reduce noise without hiding behavior. Aight, that's all. Thank you for taking your time to read this post. Feel free to give me feedback, tips, or a different perspective. I’d love to hear yours and continue the discussion. - Caddy Documentation: log - Caddy Documentation: How Logging Works Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse CODE_BLOCK: func handler(w http.ResponseWriter, r *http.Request) { hostname, _ := os.Hostname() fmt.Fprintf(w, "Hello from %s\n", hostname) } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: func handler(w http.ResponseWriter, r *http.Request) { hostname, _ := os.Hostname() fmt.Fprintf(w, "Hello from %s\n", hostname) } CODE_BLOCK: func handler(w http.ResponseWriter, r *http.Request) { hostname, _ := os.Hostname() fmt.Fprintf(w, "Hello from %s\n", hostname) } COMMAND_BLOCK: $ docker compose up -d --build $ docker logs load_balancer Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: $ docker compose up -d --build $ docker logs load_balancer COMMAND_BLOCK: $ docker compose up -d --build $ docker logs load_balancer CODE_BLOCK: {"level":"info","ts":1765883971.5864136,"msg":"maxprocs: Leaving GOMAXPROCS=4: CPU quota undefined"} {"level":"info","ts":1765883971.586685,"msg":"GOMEMLIMIT is updated","package":"github.com/KimMachineGun/automemlimit/memlimit","GOMEMLIMIT":16911289958,"previous":9223372036854775807} {"level":"info","ts":1765883971.586744,"msg":"using config from file","file":"/etc/caddy/Caddyfile"} {"level":"info","ts":1765883971.5883265,"msg":"adapted config to JSON","adapter":"caddyfile"} {"level":"warn","ts":1765883971.5883417,"msg":"Caddyfile input is not formatted; 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Linux x86_64; rv:145.0) Gecko/20100101 Firefox/145.0"],"Sec-Gpc":["1"]}},"bytes_read":0,"user_id":"","duration":0.000959646,"size":20,"status":200,"resp_headers":{"Content-Type":["text/plain; charset=utf-8"],"Via":["1.1 Caddy"],"Date":["Tue, 16 Dec 2025 11:27:04 GMT"],"Content-Length":["20"]}} {"level":"info","ts":1765884440.3606126,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49074","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"User-Agent":["curl/7.81.0"],"Accept":["*/*"]}},"bytes_read":0,"user_id":"","duration":0.000425884,"size":20,"status":200,"resp_headers":{"Date":["Tue, 16 Dec 2025 11:27:20 GMT"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"],"Via":["1.1 Caddy"]}} {"level":"info","ts":1765884442.148407,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49090","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"Accept":["*/*"],"User-Agent":["curl/7.81.0"]}},"bytes_read":0,"user_id":"","duration":0.000592974,"size":20,"status":200,"resp_headers":{"Via":["1.1 Caddy"],"Date":["Tue, 16 Dec 2025 11:27:22 GMT"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"]}} {"level":"info","ts":1765884442.6677225,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49102","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"User-Agent":["curl/7.81.0"],"Accept":["*/*"]}},"bytes_read":0,"user_id":"","duration":0.000432397,"size":20,"status":200,"resp_headers":{"Via":["1.1 Caddy"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"],"Date":["Tue, 16 Dec 2025 11:27:22 GMT"]}} {"level":"info","ts":1765884443.2411807,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49106","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"Accept":["*/*"],"User-Agent":["curl/7.81.0"]}},"bytes_read":0,"user_id":"","duration":0.000496529,"size":20,"status":200,"resp_headers":{"Content-Type":["text/plain; charset=utf-8"],"Date":["Tue, 16 Dec 2025 11:27:23 GMT"],"Via":["1.1 Caddy"],"Content-Length":["20"]}} CODE_BLOCK: {"level":"info","ts":1765884414.2170205,"logger":"tls","msg":"cleaning storage unit","storage":"FileStorage:/data/caddy"} {"level":"info","ts":1765884414.2187994,"logger":"tls","msg":"finished cleaning storage units"} {"level":"info","ts":1765884423.2440372,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"51346","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"Sec-Fetch-Mode":["navigate"],"Sec-Gpc":["1"],"Connection":["keep-alive"],"Priority":["u=0, i"],"Accept":["text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"],"Sec-Fetch-Dest":["document"],"Sec-Fetch-Site":["none"],"User-Agent":["Mozilla/5.0 (X11; Linux x86_64; rv:145.0) Gecko/20100101 Firefox/145.0"],"Sec-Fetch-User":["?1"],"Accept-Language":["en-US,en;q=0.5"],"Accept-Encoding":["gzip, deflate, br, zstd"],"Upgrade-Insecure-Requests":["1"]}},"bytes_read":0,"user_id":"","duration":0.000733253,"size":20,"status":200,"resp_headers":{"Content-Length":["20"],"Via":["1.1 Caddy"],"Content-Type":["text/plain; charset=utf-8"],"Date":["Tue, 16 Dec 2025 11:27:03 GMT"]}} {"level":"info","ts":1765884423.7748682,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"51346","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"User-Agent":["Mozilla/5.0 (X11; Linux x86_64; rv:145.0) Gecko/20100101 Firefox/145.0"],"Sec-Fetch-User":["?1"],"Sec-Gpc":["1"],"Upgrade-Insecure-Requests":["1"],"Sec-Fetch-Dest":["document"],"Sec-Fetch-Site":["none"],"Accept-Language":["en-US,en;q=0.5"],"Accept-Encoding":["gzip, deflate, br, zstd"],"Priority":["u=0, i"],"Accept":["text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"],"Connection":["keep-alive"],"Sec-Fetch-Mode":["navigate"]}},"bytes_read":0,"user_id":"","duration":0.000783659,"size":20,"status":200,"resp_headers":{"Via":["1.1 Caddy"],"Date":["Tue, 16 Dec 2025 11:27:03 GMT"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"]}} {"level":"info","ts":1765884424.1060758,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"51346","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"Upgrade-Insecure-Requests":["1"],"Sec-Fetch-Site":["none"],"Accept-Language":["en-US,en;q=0.5"],"Sec-Gpc":["1"],"Sec-Fetch-Dest":["document"],"Sec-Fetch-User":["?1"],"User-Agent":["Mozilla/5.0 (X11; Linux x86_64; rv:145.0) Gecko/20100101 Firefox/145.0"],"Accept":["text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"],"Accept-Encoding":["gzip, deflate, br, zstd"],"Sec-Fetch-Mode":["navigate"],"Priority":["u=0, i"],"Connection":["keep-alive"]}},"bytes_read":0,"user_id":"","duration":0.002117571,"size":20,"status":200,"resp_headers":{"Via":["1.1 Caddy"],"Date":["Tue, 16 Dec 2025 11:27:04 GMT"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"]}} {"level":"info","ts":1765884424.456112,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"51346","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"Connection":["keep-alive"],"Upgrade-Insecure-Requests":["1"],"Sec-Fetch-Site":["none"],"Sec-Fetch-User":["?1"],"Priority":["u=0, i"],"Accept-Language":["en-US,en;q=0.5"],"Sec-Fetch-Mode":["navigate"],"Accept":["text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"],"Accept-Encoding":["gzip, deflate, br, zstd"],"Sec-Fetch-Dest":["document"],"User-Agent":["Mozilla/5.0 (X11; Linux x86_64; rv:145.0) Gecko/20100101 Firefox/145.0"],"Sec-Gpc":["1"]}},"bytes_read":0,"user_id":"","duration":0.000959646,"size":20,"status":200,"resp_headers":{"Content-Type":["text/plain; charset=utf-8"],"Via":["1.1 Caddy"],"Date":["Tue, 16 Dec 2025 11:27:04 GMT"],"Content-Length":["20"]}} {"level":"info","ts":1765884440.3606126,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49074","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"User-Agent":["curl/7.81.0"],"Accept":["*/*"]}},"bytes_read":0,"user_id":"","duration":0.000425884,"size":20,"status":200,"resp_headers":{"Date":["Tue, 16 Dec 2025 11:27:20 GMT"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"],"Via":["1.1 Caddy"]}} {"level":"info","ts":1765884442.148407,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49090","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"Accept":["*/*"],"User-Agent":["curl/7.81.0"]}},"bytes_read":0,"user_id":"","duration":0.000592974,"size":20,"status":200,"resp_headers":{"Via":["1.1 Caddy"],"Date":["Tue, 16 Dec 2025 11:27:22 GMT"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"]}} {"level":"info","ts":1765884442.6677225,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49102","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"User-Agent":["curl/7.81.0"],"Accept":["*/*"]}},"bytes_read":0,"user_id":"","duration":0.000432397,"size":20,"status":200,"resp_headers":{"Via":["1.1 Caddy"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"],"Date":["Tue, 16 Dec 2025 11:27:22 GMT"]}} {"level":"info","ts":1765884443.2411807,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"172.21.0.1","remote_port":"49106","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"Accept":["*/*"],"User-Agent":["curl/7.81.0"]}},"bytes_read":0,"user_id":"","duration":0.000496529,"size":20,"status":200,"resp_headers":{"Content-Type":["text/plain; charset=utf-8"],"Date":["Tue, 16 Dec 2025 11:27:23 GMT"],"Via":["1.1 Caddy"],"Content-Length":["20"]}} COMMAND_BLOCK: docker logs -f load_balancer 2>&1 | jq -R 'fromjson? | {level, logger, msg, request: {method: .request.method, uri: .request.uri}, status, duration}' Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: docker logs -f load_balancer 2>&1 | jq -R 'fromjson? | {level, logger, msg, request: {method: .request.method, uri: .request.uri}, status, duration}' COMMAND_BLOCK: docker logs -f load_balancer 2>&1 | jq -R 'fromjson? | {level, logger, msg, request: {method: .request.method, uri: .request.uri}, status, duration}' CODE_BLOCK: ... { "level": "info", "logger": "tls", "msg": "finished cleaning storage units", "request": { "method": null, "uri": null }, "status": null, "duration": null } { "level": "info", "logger": "http.log.access.log0", "msg": "handled request", "request": { "method": "GET", "uri": "/" }, "status": 200, "duration": 0.000733253 } ... Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: ... { "level": "info", "logger": "tls", "msg": "finished cleaning storage units", "request": { "method": null, "uri": null }, "status": null, "duration": null } { "level": "info", "logger": "http.log.access.log0", "msg": "handled request", "request": { "method": "GET", "uri": "/" }, "status": 200, "duration": 0.000733253 } ... CODE_BLOCK: ... { "level": "info", "logger": "tls", "msg": "finished cleaning storage units", "request": { "method": null, "uri": null }, "status": null, "duration": null } { "level": "info", "logger": "http.log.access.log0", "msg": "handled request", "request": { "method": "GET", "uri": "/" }, "status": 200, "duration": 0.000733253 } ... CODE_BLOCK: { log { level DEBUG format json } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: { log { level DEBUG format json } } CODE_BLOCK: { log { level DEBUG format json } } CODE_BLOCK: {"level":"debug","logger":"http.handlers.reverse_proxy","msg":"selected upstream","dial":"worker_3:8081","total_upstreams":3} Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: {"level":"debug","logger":"http.handlers.reverse_proxy","msg":"selected upstream","dial":"worker_3:8081","total_upstreams":3} CODE_BLOCK: {"level":"debug","logger":"http.handlers.reverse_proxy","msg":"selected upstream","dial":"worker_3:8081","total_upstreams":3} COMMAND_BLOCK: $ docker stop worker_2 Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: $ docker stop worker_2 COMMAND_BLOCK: $ docker stop worker_2 COMMAND_BLOCK: $ curl http://localhost:8082 Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: $ curl http://localhost:8082 COMMAND_BLOCK: $ curl http://localhost:8082 CODE_BLOCK: Hello from worker_3 Hello from worker_1 Hello from worker_3 Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: Hello from worker_3 Hello from worker_1 Hello from worker_3 CODE_BLOCK: Hello from worker_3 Hello from worker_1 Hello from worker_3 CODE_BLOCK: {: dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992098.8407533,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992101.6597724,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992104.640808,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: {: dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992098.8407533,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992101.6597724,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992104.640808,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} CODE_BLOCK: {: dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992098.8407533,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992101.6597724,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} {"level":"info","ts":1765992104.640808,"logger":"http.handlers.reverse_proxy.health_checker.active","msg":"HTTP request failed","host":"worker_2:8081","error":"Get \"http://worker_2:8081/\": dial tcp: lookup worker_2 on 127.0.0.11:53: no such host"} CODE_BLOCK: { log { level INFO format json } } :80 { log { output stdout format console } reverse_proxy worker_1:8081 worker_2:8081 worker_3:8081 { lb_policy random health_uri / health_interval 3s } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: { log { level INFO format json } } :80 { log { output stdout format console } reverse_proxy worker_1:8081 worker_2:8081 worker_3:8081 { lb_policy random health_uri / health_interval 3s } } CODE_BLOCK: { log { level INFO format json } } :80 { log { output stdout format console } reverse_proxy worker_1:8081 worker_2:8081 worker_3:8081 { lb_policy random health_uri / health_interval 3s } } COMMAND_BLOCK: $ docker restart load_balancer Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: $ docker restart load_balancer COMMAND_BLOCK: $ docker restart load_balancer COMMAND_BLOCK: $ docker logs load_balancer Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: $ docker logs load_balancer COMMAND_BLOCK: $ docker logs load_balancer CODE_BLOCK: 2025/12/17 17:31:44.788 INFO http.log.access.log0 handled request {"request": {"remote_ip": "172.21.0.1", "remote_port": "36598", "client_ip": "172.21.0.1", "proto": "HTTP/1.1", "method": "GET", "host": "localhost:8082", "uri": "/", "headers": {"User-Agent": ["curl/7.81.0"], "Accept": ["*/*"]}}, "bytes_read": 0, "user_id": "", "duration": 0.001321876, "size": 20, "status": 200, "resp_headers": {"Date": ["Wed, 17 Dec 2025 17:31:44 GMT"], "Content-Length": ["20"], "Content-Type": ["text/plain; charset=utf-8"], "Via": ["1.1 Caddy"]}} Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: 2025/12/17 17:31:44.788 INFO http.log.access.log0 handled request {"request": {"remote_ip": "172.21.0.1", "remote_port": "36598", "client_ip": "172.21.0.1", "proto": "HTTP/1.1", "method": "GET", "host": "localhost:8082", "uri": "/", "headers": {"User-Agent": ["curl/7.81.0"], "Accept": ["*/*"]}}, "bytes_read": 0, "user_id": "", "duration": 0.001321876, "size": 20, "status": 200, "resp_headers": {"Date": ["Wed, 17 Dec 2025 17:31:44 GMT"], "Content-Length": ["20"], "Content-Type": ["text/plain; charset=utf-8"], "Via": ["1.1 Caddy"]}} CODE_BLOCK: 2025/12/17 17:31:44.788 INFO http.log.access.log0 handled request {"request": {"remote_ip": "172.21.0.1", "remote_port": "36598", "client_ip": "172.21.0.1", "proto": "HTTP/1.1", "method": "GET", "host": "localhost:8082", "uri": "/", "headers": {"User-Agent": ["curl/7.81.0"], "Accept": ["*/*"]}}, "bytes_read": 0, "user_id": "", "duration": 0.001321876, "size": 20, "status": 200, "resp_headers": {"Date": ["Wed, 17 Dec 2025 17:31:44 GMT"], "Content-Length": ["20"], "Content-Type": ["text/plain; charset=utf-8"], "Via": ["1.1 Caddy"]}} CODE_BLOCK: ... { log { output stdout format json { time_format "2006-01-02 15:04:05 MST" time_local duration_format "ms" level_format "upper" } } } Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: ... { log { output stdout format json { time_format "2006-01-02 15:04:05 MST" time_local duration_format "ms" level_format "upper" } } } CODE_BLOCK: ... { log { output stdout format json { time_format "2006-01-02 15:04:05 MST" time_local duration_format "ms" level_format "upper" } } } CODE_BLOCK: {sp_headers":{"Via":["1.1 Caddy"],"Content-Type":["text/plain; charset=utf-8"],"Date":["Wed, 17 Dec 2025 17:36:47 GMT"],"Content-Length":["20"]}} {"level":"debug","ts":1765993007.632117,"logger":"http.handlers.reverse_proxy","msg":"selected upstream","dial":"worker_1:8081","total_upstreams":3} {"level":"debug","ts":1765993007.6339025,"logger":"http.handlers.reverse_proxy","msg":"upstream roundtrip","upstream":"worker_1:8081","duration":0.001633852,"request":{"remote_ip":"172.21.0.1","remote_port":"36378","client_ip":"172.21.0.1","proto":"HTTP/1.1","method":"GET","host":"localhost:8082","uri":"/","headers":{"X-Forwarded-For":["172.21.0.1"],"X-Forwarded-Proto":["http"],"X-Forwarded-Host":["localhost:8082"],"Via":["1.1 Caddy"],"User-Agent":["curl/7.81.0"],"Accept":["*/*"]}},"headers":{"Date":["Wed, 17 Dec 2025 17:36:47 GMT"],"Content-Length":["20"],"Content-Type":["text/plain; charset=utf-8"]},"status":200} {"level":"INFO","ts":"2025-12-17 17:36:47 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