Modernize code, fix linter errors

Signed-off-by: Knut Ahlers <knut@ahlers.me>

.golangci.yml

@@ -0,0 +1,176 @@
+# Derived from https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml
+
+---
+
+run:
+  # timeout for analysis, e.g. 30s, 5m, default is 1m
+  timeout: 5m
+  # Force readonly modules usage for checking
+  modules-download-mode: readonly
+
+output:
+  formats:
+    - format: tab
+      path: stdout
+
+issues:
+  # This disables the included exclude-list in golangci-lint as that
+  # list for example fully hides G304 gosec rule, errcheck, exported
+  # rule of revive and other errors one really wants to see.
+  # Smme detail: https://github.com/golangci/golangci-lint/issues/456
+  exclude-use-default: false
+  # Don't limit the number of shown issues: Report ALL of them
+  max-issues-per-linter: 0
+  max-same-issues: 0
+
+linters:
+  disable-all: true
+  enable:
+    - asciicheck    # Simple linter to check that your code does not contain non-ASCII identifiers [fast: true, auto-fix: false]
+    - bidichk       # Checks for dangerous unicode character sequences [fast: true, auto-fix: false]
+    - bodyclose     # checks whether HTTP response body is closed successfully [fast: true, auto-fix: false]
+    - containedctx  # containedctx is a linter that detects struct contained context.Context field [fast: true, auto-fix: false]
+    - contextcheck  # check the function whether use a non-inherited context [fast: false, auto-fix: false]
+    - dogsled       # Checks assignments with too many blank identifiers (e.g. x, _, _, _, := f()) [fast: true, auto-fix: false]
+    - durationcheck # check for two durations multiplied together [fast: false, auto-fix: false]
+    - errcheck      # Errcheck is a program for checking for unchecked errors in go programs. These unchecked errors can be critical bugs in some cases [fast: false, auto-fix: false]
+    - errchkjson    # Checks types passed to the json encoding functions. Reports unsupported types and optionally reports occations, where the check for the returned error can be omitted. [fast: false, auto-fix: false]
+    - exportloopref # checks for pointers to enclosing loop variables [fast: true, auto-fix: false]
+    - forbidigo     # Forbids identifiers [fast: true, auto-fix: false]
+    - funlen        # Tool for detection of long functions [fast: true, auto-fix: false]
+    - gocognit      # Computes and checks the cognitive complexity of functions [fast: true, auto-fix: false]
+    - goconst       # Finds repeated strings that could be replaced by a constant [fast: true, auto-fix: false]
+    - gocritic      # The most opinionated Go source code linter [fast: true, auto-fix: false]
+    - gocyclo       # Computes and checks the cyclomatic complexity of functions [fast: true, auto-fix: false]
+    - godox         # Tool for detection of FIXME, TODO and other comment keywords [fast: true, auto-fix: false]
+    - gofmt         # Gofmt checks whether code was gofmt-ed. By default this tool runs with -s option to check for code simplification [fast: true, auto-fix: true]
+    - gofumpt       # Gofumpt checks whether code was gofumpt-ed. [fast: true, auto-fix: true]
+    - goimports     # Goimports does everything that gofmt does. Additionally it checks unused imports [fast: true, auto-fix: true]
+    - gomnd         # An analyzer to detect magic numbers. [fast: true, auto-fix: false]
+    - gosec         # Inspects source code for security problems [fast: true, auto-fix: false]
+    - gosimple      # Linter for Go source code that specializes in simplifying a code [fast: true, auto-fix: false]
+    - govet         # Vet examines Go source code and reports suspicious constructs, such as Printf calls whose arguments do not align with the format string [fast: true, auto-fix: false]
+    - ineffassign   # Detects when assignments to existing variables are not used [fast: true, auto-fix: false]
+    - misspell      # Finds commonly misspelled English words in comments [fast: true, auto-fix: true]
+    - nakedret      # Finds naked returns in functions greater than a specified function length [fast: true, auto-fix: false]
+    - nilerr        # Finds the code that returns nil even if it checks that the error is not nil. [fast: false, auto-fix: false]
+    - nilnil        # Checks that there is no simultaneous return of `nil` error and an invalid value. [fast: false, auto-fix: false]
+    - noctx         # noctx finds sending http request without context.Context [fast: true, auto-fix: false]
+    - nolintlint    # Reports ill-formed or insufficient nolint directives [fast: true, auto-fix: false]
+    - revive        # Fast, configurable, extensible, flexible, and beautiful linter for Go. Drop-in replacement of golint. [fast: false, auto-fix: false]
+    - staticcheck   # Staticcheck is a go vet on steroids, applying a ton of static analysis checks [fast: true, auto-fix: false]
+    - stylecheck    # Stylecheck is a replacement for golint [fast: true, auto-fix: false]
+    - tenv          # tenv is analyzer that detects using os.Setenv instead of t.Setenv since Go1.17 [fast: false, auto-fix: false]
+    - typecheck     # Like the front-end of a Go compiler, parses and type-checks Go code [fast: true, auto-fix: false]
+    - unconvert     # Remove unnecessary type conversions [fast: true, auto-fix: false]
+    - unused        # Checks Go code for unused constants, variables, functions and types [fast: false, auto-fix: false]
+    - wastedassign  # wastedassign finds wasted assignment statements. [fast: false, auto-fix: false]
+    - wrapcheck     # Checks that errors returned from external packages are wrapped [fast: false, auto-fix: false]
+
+linters-settings:
+  funlen:
+    lines: 100
+    statements: 60
+
+  gocyclo:
+    # minimal code complexity to report, 30 by default (but we recommend 10-20)
+    min-complexity: 15
+
+  gomnd:
+    settings:
+      mnd:
+        ignored-functions: 'strconv.(?:Format|Parse)\B+'
+
+  revive:
+    rules:
+      #- name: add-constant           # Suggests using constant for magic numbers and string literals
+                                      # Opinion: Makes sense for strings, not for numbers but checks numbers
+      #- name: argument-limit         # Specifies the maximum number of arguments a function can receive | Opinion: Don't need this
+      - name: atomic                  # Check for common mistaken usages of the `sync/atomic` package
+      - name: banned-characters       # Checks banned characters in identifiers
+        arguments:
+          - ';' # Greek question mark
+      - name: bare-return             # Warns on bare returns
+      - name: blank-imports           # Disallows blank imports
+      - name: bool-literal-in-expr    # Suggests removing Boolean literals from logic expressions
+      - name: call-to-gc              # Warns on explicit call to the garbage collector
+      #- name: cognitive-complexity   # Sets restriction for maximum Cognitive complexity.
+                                      # There is a dedicated linter for this
+      - name: confusing-naming        # Warns on methods with names that differ only by capitalization
+      - name: confusing-results       # Suggests to name potentially confusing function results
+      - name: constant-logical-expr   # Warns on constant logical expressions
+      - name: context-as-argument     # `context.Context` should be the first argument of a function.
+      - name: context-keys-type       # Disallows the usage of basic types in `context.WithValue`.
+      #- name: cyclomatic             # Sets restriction for maximum Cyclomatic complexity.
+                                      # There is a dedicated linter for this
+      #- name: datarace               # Spots potential dataraces
+                                      # Is not (yet) available?
+      - name: deep-exit               # Looks for program exits in funcs other than `main()` or `init()`
+      - name: defer                   # Warns on some [defer gotchas](https://blog.learngoprogramming.com/5-gotchas-of-defer-in-go-golang-part-iii-36a1ab3d6ef1)
+      - name: dot-imports             # Forbids `.` imports.
+      - name: duplicated-imports      # Looks for packages that are imported two or more times
+      - name: early-return            # Spots if-then-else statements that can be refactored to simplify code reading
+      - name: empty-block             # Warns on empty code blocks
+      - name: empty-lines             # Warns when there are heading or trailing newlines in a block
+      - name: errorf                  # Should replace `errors.New(fmt.Sprintf())` with `fmt.Errorf()`
+      - name: error-naming            # Naming of error variables.
+      - name: error-return            # The error return parameter should be last.
+      - name: error-strings           # Conventions around error strings.
+      - name: exported                # Naming and commenting conventions on exported symbols.
+        arguments: ['sayRepetitiveInsteadOfStutters']
+      #- name: file-header            # Header which each file should have.
+                                      # Useless without config, have no config for it
+      - name: flag-parameter          # Warns on boolean parameters that create a control coupling
+      #- name: function-length        # Warns on functions exceeding the statements or lines max
+                                      # There is a dedicated linter for this
+      #- name: function-result-limit  # Specifies the maximum number of results a function can return
+                                      # Opinion: Don't need this
+      - name: get-return              # Warns on getters that do not yield any result
+      - name: identical-branches      # Spots if-then-else statements with identical `then` and `else` branches
+      - name: if-return               # Redundant if when returning an error.
+      #- name: imports-blacklist      # Disallows importing the specified packages
+                                      # Useless without config, have no config for it
+      - name: import-shadowing        # Spots identifiers that shadow an import
+      - name: increment-decrement     # Use `i++` and `i--` instead of `i += 1` and `i -= 1`.
+      - name: indent-error-flow       # Prevents redundant else statements.
+      #- name: line-length-limit      # Specifies the maximum number of characters in a lined
+                                      # There is a dedicated linter for this
+      #- name: max-public-structs     # The maximum number of public structs in a file.
+                                      # Opinion: Don't need this
+      - name: modifies-parameter      # Warns on assignments to function parameters
+      - name: modifies-value-receiver # Warns on assignments to value-passed method receivers
+      #- name: nested-structs         # Warns on structs within structs
+                                      # Opinion: Don't need this
+      - name: optimize-operands-order # Checks inefficient conditional expressions
+      #- name: package-comments       # Package commenting conventions.
+                                      # Opinion: Don't need this
+      - name: range                   # Prevents redundant variables when iterating over a collection.
+      - name: range-val-address       # Warns if address of range value is used dangerously
+      - name: range-val-in-closure    # Warns if range value is used in a closure dispatched as goroutine
+      - name: receiver-naming         # Conventions around the naming of receivers.
+      - name: redefines-builtin-id    # Warns on redefinitions of builtin identifiers
+      #- name: string-format          # Warns on specific string literals that fail one or more user-configured regular expressions
+                                      # Useless without config, have no config for it
+      - name: string-of-int           # Warns on suspicious casts from int to string
+      - name: struct-tag              # Checks common struct tags like `json`,`xml`,`yaml`
+      - name: superfluous-else        # Prevents redundant else statements (extends indent-error-flow)
+      - name: time-equal              # Suggests to use `time.Time.Equal` instead of `==` and `!=` for equality check time.
+      - name: time-naming             # Conventions around the naming of time variables.
+      - name: unconditional-recursion # Warns on function calls that will lead to (direct) infinite recursion
+      - name: unexported-naming       # Warns on wrongly named un-exported symbols
+      - name: unexported-return       # Warns when a public return is from unexported type.
+      - name: unhandled-error         # Warns on unhandled errors returned by funcion calls
+        arguments:
+          - "fmt.(Fp|P)rint(f|ln|)"
+      - name: unnecessary-stmt        # Suggests removing or simplifying unnecessary statements
+      - name: unreachable-code        # Warns on unreachable code
+      - name: unused-parameter        # Suggests to rename or remove unused function parameters
+      - name: unused-receiver         # Suggests to rename or remove unused method receivers
+      #- name: use-any                # Proposes to replace `interface{}` with its alias `any`
+                                      # Is not (yet) available?
+      - name: useless-break           # Warns on useless `break` statements in case clauses
+      - name: var-declaration         # Reduces redundancies around variable declaration.
+      - name: var-naming              # Naming rules.
+      - name: waitgroup-by-value      # Warns on functions taking sync.WaitGroup as a by-value parameter
+
+...

checks.go

@@ -0,0 +1,151 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"os/exec"
+	"time"
+
+	"github.com/sirupsen/logrus"
+	"golang.org/x/net/context"
+	"gopkg.in/yaml.v3"
+)
+
+const (
+	checkKillWait            = 100 * time.Millisecond
+	remoteConfigFetchTimeout = 2 * time.Second
+)
+
+type (
+	checkCommand struct {
+		Name     string `yaml:"name"`
+		Command  string `yaml:"command"`
+		WarnOnly bool   `yaml:"warn_only"`
+	}
+
+	checkResult struct {
+		Check     checkCommand
+		IsSuccess bool
+		Streak    int64
+	}
+)
+
+func executeAndRegisterCheck(ctx context.Context, checkID string) {
+	var (
+		check  = checks[checkID]
+		logger = logrus.WithField("check_id", checkID)
+	)
+
+	cmd := exec.Command("/bin/bash", "-e", "-o", "pipefail", "-c", check.Command) //#nosec G204 // Intended to run an user-defined command
+	cmd.Stderr = logger.WithField("stream", "STDERR").Writer()
+	if cfg.Verbose {
+		cmd.Stdout = logger.WithField("stream", "STDOUT").Writer()
+	}
+	err := cmd.Start()
+
+	if err == nil {
+		cmdDone := make(chan error)
+		go func(cmdDone chan error, cmd *exec.Cmd) { cmdDone <- cmd.Wait() }(cmdDone, cmd)
+		loop := true
+		for loop {
+			select {
+			case err = <-cmdDone:
+				loop = false
+			case <-ctx.Done():
+				logger.Error("execution of check will be killed through context timeout")
+				if err := cmd.Process.Kill(); err != nil {
+					logger.WithError(err).Error("killing check command")
+				}
+				time.Sleep(checkKillWait)
+			}
+		}
+	}
+
+	success := err == nil
+
+	checkResultsLock.Lock()
+
+	if _, ok := checkResults[checkID]; !ok {
+		checkResults[checkID] = &checkResult{
+			Check: check,
+		}
+	}
+
+	if success == checkResults[checkID].IsSuccess {
+		checkResults[checkID].Streak++
+	} else {
+		checkResults[checkID].IsSuccess = success
+		checkResults[checkID].Streak = 1
+	}
+
+	if !success {
+		logger.WithError(err).WithField("streak", checkResults[checkID].Streak).Warn("check failed, streak increased")
+	}
+
+	lastResultRegistered = time.Now()
+
+	checkResultsLock.Unlock()
+}
+
+func loadChecks() error {
+	var rawChecks io.Reader
+
+	if _, err := os.Stat(cfg.CheckDefinitionsFile); err == nil {
+		// We got a local file, read it
+		f, err := os.Open(cfg.CheckDefinitionsFile)
+		if err != nil {
+			return fmt.Errorf("opening file: %w", err)
+		}
+		defer func() {
+			if err := f.Close(); err != nil {
+				logrus.WithError(err).Error("closing configfile (leaked fd)")
+			}
+		}()
+		rawChecks = f
+	} else {
+		// Check whether we got an URL
+		if _, err := url.Parse(cfg.CheckDefinitionsFile); err != nil {
+			return errors.New("definitions file is neither a local file nor a URL")
+		}
+
+		// We got an URL, fetch and read it
+		ctx, cancel := context.WithTimeout(context.TODO(), remoteConfigFetchTimeout)
+		defer cancel()
+
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, cfg.CheckDefinitionsFile, nil)
+		if err != nil {
+			return fmt.Errorf("creating request: %w", err)
+		}
+
+		resp, err := http.DefaultClient.Do(req)
+		if err != nil {
+			return fmt.Errorf("executing request: %w", err)
+		}
+		defer func() {
+			if err := resp.Body.Close(); err != nil {
+				logrus.WithError(err).Error("closing configfile request body (leaked fd)")
+			}
+		}()
+		rawChecks = resp.Body
+	}
+
+	tmpResult := map[string]checkCommand{}
+	if err := yaml.NewDecoder(rawChecks).Decode(&tmpResult); err != nil {
+		return fmt.Errorf("decoding checks file: %w", err)
+	}
+
+	checks = tmpResult
+	return nil
+}
+
+func spawnChecks() {
+	ctx, _ := context.WithTimeout(context.Background(), cfg.CheckInterval-time.Second)
+
+	for id := range checks {
+		go executeAndRegisterCheck(ctx, id)
+	}
+}

go.mod

@@ -4,14 +4,14 @@ go 1.22.1
 
 require (
 	github.com/Luzifer/rconfig/v2 v2.5.0
-	github.com/gorilla/mux v1.8.1
 	github.com/robfig/cron/v3 v3.0.1
+	github.com/sirupsen/logrus v1.9.3
 	golang.org/x/net v0.22.0
-	gopkg.in/yaml.v2 v2.4.0
+	gopkg.in/yaml.v3 v3.0.1
 )
 
 require (
 	github.com/spf13/pflag v1.0.5 // indirect
+	golang.org/x/sys v0.18.0 // indirect
 	gopkg.in/validator.v2 v2.0.1 // indirect
-	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,9 +1,8 @@
 github.com/Luzifer/rconfig/v2 v2.5.0 h1:zx5lfQbNX3za4VegID97IeY+M+BmfgHxWJTYA94sxok=
 github.com/Luzifer/rconfig/v2 v2.5.0/go.mod h1:eGWUPQeCPv/Pr/p0hjmwFgI20uqvwi/Szen69hUzGzU=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/gorilla/mux v1.8.1 h1:TuBL49tXwgrFYWhqrNgrUNEY92u81SPhu7sTdzQEiWY=
-github.com/gorilla/mux v1.8.1/go.mod h1:AKf9I4AEqPTmMytcMc0KkNouC66V3BtZ4qD5fmWSiMQ=
 github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
 github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
@@ -12,18 +11,24 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/robfig/cron/v3 v3.0.1 h1:WdRxkvbJztn8LMz/QEvLN5sBU+xKpSqwwUO1Pjr4qDs=
 github.com/robfig/cron/v3 v3.0.1/go.mod h1:eQICP3HwyT7UooqI/z+Ov+PtYAWygg1TEWWzGIFLtro=
+github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
+github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
 github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
 golang.org/x/net v0.22.0 h1:9sGLhx7iRIHEiX0oAJ3MRZMUCElJgy7Br1nO+AMN3Tc=
 golang.org/x/net v0.22.0/go.mod h1:JKghWKKOSdJwpW2GEx0Ja7fmaKnMsbu+MWVZTokSYmg=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.18.0 h1:DBdB3niSjOA/O0blCZBqDefyWNYveAYMNF1Wum0DYQ4=
+golang.org/x/sys v0.18.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
 gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
 gopkg.in/validator.v2 v2.0.1 h1:xF0KWyGWXm/LM2G1TrEjqOu4pa6coO9AlWSf3msVfDY=
 gopkg.in/validator.v2 v2.0.1/go.mod h1:lIUZBlB3Im4s/eYp39Ry/wkR02yOPhZ9IwIRBjuPuG8=
-gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
-gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

main.go

@@ -2,22 +2,16 @@ package main
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 	"io"
-	"log"
 	"net/http"
-	"net/url"
 	"os"
-	"os/exec"
 	"strconv"
 	"sync"
 	"time"
 
-	"github.com/gorilla/mux"
 	"github.com/robfig/cron/v3"
-	"golang.org/x/net/context"
-	"gopkg.in/yaml.v2"
+	"github.com/sirupsen/logrus"
 
 	"github.com/Luzifer/rconfig/v2"
 )
@@ -30,7 +24,8 @@ var (
 		CheckInterval         time.Duration `flag:"check-interval" default:"1m" description:"How often to execute checks (do not set below 10s!)"`
 		ConfigRefreshInterval time.Duration `flag:"config-refresh" default:"10m" description:"How often to update checks from definitions file / url"`
 
-		Verbose bool `flag:"verbose,v" default:"false" description:"Attach stdout of the executed commands"`
+		Verbose  bool   `flag:"verbose,v" default:"false" description:"Attach stdout of the executed commands"`
+		LogLevel string `flag:"log-level" default:"info" description:"Log level (debug, info, warn, error, fatal)"`
 
 		Listen         string `flag:"listen" default:":3000" description:"IP/Port to listen on for ELB health checks"`
 		VersionAndExit bool   `flag:"version" default:"false" description:"Print version and exit"`
@@ -44,157 +39,73 @@ var (
 	lastResultRegistered time.Time
 )
 
-type checkCommand struct {
-	Name        string `yaml:"name"`
-	Command     string `yaml:"command"`
-	WarnOnly    bool   `yaml:"warn_only"`
-	WarnOnlyOld *bool  `yaml:"warn-only"`
-}
-
-type checkResult struct {
-	Check     checkCommand
-	IsSuccess bool
-	Streak    int64
-}
-
-func init() {
-	rconfig.Parse(&cfg)
-
-	if cfg.VersionAndExit {
-		fmt.Printf("elb-instance-status %s\n", version)
-		os.Exit(0)
-	}
-}
-
-func loadChecks() error {
-	var rawChecks io.Reader
-
-	if _, err := os.Stat(cfg.CheckDefinitionsFile); err == nil {
-		// We got a local file, read it
-		f, err := os.Open(cfg.CheckDefinitionsFile)
-		if err != nil {
-			return err
-		}
-		defer f.Close()
-		rawChecks = f
-	} else {
-		// Check whether we got an URL
-		if _, err := url.Parse(cfg.CheckDefinitionsFile); err != nil {
-			return errors.New("Definitions file is neither a local file nor a URL")
-		}
-
-		// We got an URL, fetch and read it
-		resp, err := http.Get(cfg.CheckDefinitionsFile)
-		if err != nil {
-			return err
-		}
-		defer resp.Body.Close()
-		rawChecks = resp.Body
+func initApp() (err error) {
+	rconfig.AutoEnv(true)
+	if err = rconfig.Parse(&cfg); err != nil {
+		return fmt.Errorf("parsing CLI options: %w", err)
 	}
 
-	tmpResult := map[string]checkCommand{}
-	if err := yaml.NewDecoder(rawChecks).Decode(&tmpResult); err != nil {
-		return err
+	l, err := logrus.ParseLevel(cfg.LogLevel)
+	if err != nil {
+		return fmt.Errorf("parsing log-level: %w", err)
 	}
+	logrus.SetLevel(l)
 
-	for name, check := range tmpResult {
-		if check.WarnOnlyOld != nil {
-			log.Printf("Parameter 'warn-only' in check %q is deprecated: It's now named 'warn_only'", name)
-			check.WarnOnly = *check.WarnOnlyOld
-		}
-	}
-
-	checks = tmpResult
 	return nil
 }
 
 func main() {
-	if err := loadChecks(); err != nil {
-		log.Fatalf("Unable to read definitions file: %s", err)
+	var err error
+	if err = initApp(); err != nil {
+		logrus.WithError(err).Fatal("initializing app")
+	}
+
+	if cfg.VersionAndExit {
+		fmt.Printf("elb-instance-status %s\n", version) //nolint:forbidigo
+		os.Exit(0)
+	}
+
+	if err = loadChecks(); err != nil {
+		logrus.WithError(err).Fatal("reading definitions file")
 	}
 
 	c := cron.New()
-	c.AddFunc("@every "+cfg.CheckInterval.String(), spawnChecks)
-	c.AddFunc("@every "+cfg.ConfigRefreshInterval.String(), func() {
+
+	if _, err = c.AddFunc(fmt.Sprintf("@every %s", cfg.CheckInterval), spawnChecks); err != nil {
+		logrus.WithError(err).Fatal("registering spawn function")
+	}
+
+	if _, err = c.AddFunc(fmt.Sprintf("@every %s", cfg.ConfigRefreshInterval), func() {
 		if err := loadChecks(); err != nil {
-			log.Printf("Unable to refresh checks: %s", err)
+			logrus.WithError(err).Error("refreshing checks")
 		}
-	})
+	}); err != nil {
+		logrus.WithError(err).Fatal("registering config-refresh function")
+	}
+
 	c.Start()
 
 	spawnChecks()
 
-	r := mux.NewRouter()
-	r.HandleFunc("/status", handleELBHealthCheck)
-	if err := http.ListenAndServe(cfg.Listen, r); err != nil {
-		log.Fatalf("Unable to listen: %s", err)
+	http.HandleFunc("/status", handleELBHealthCheck)
+
+	server := &http.Server{
+		Addr:              cfg.Listen,
+		Handler:           http.DefaultServeMux,
+		ReadHeaderTimeout: time.Second,
+	}
+
+	if err = server.ListenAndServe(); err != nil {
+		logrus.WithError(err).Fatal("listening for HTTP traffic")
 	}
 }
 
-func spawnChecks() {
-	ctx, _ := context.WithTimeout(context.Background(), cfg.CheckInterval-time.Second)
-
-	for id := range checks {
-		go executeAndRegisterCheck(ctx, id)
-	}
-}
-
-func executeAndRegisterCheck(ctx context.Context, checkID string) {
-	check := checks[checkID]
-
-	cmd := exec.Command("/bin/bash", "-e", "-o", "pipefail", "-c", check.Command)
-	cmd.Stderr = newPrefixedLogger(os.Stderr, checkID+":STDERR")
-	if cfg.Verbose {
-		cmd.Stdout = newPrefixedLogger(os.Stderr, checkID+":STDOUT")
-	}
-	err := cmd.Start()
-
-	if err == nil {
-		cmdDone := make(chan error)
-		go func(cmdDone chan error, cmd *exec.Cmd) { cmdDone <- cmd.Wait() }(cmdDone, cmd)
-		loop := true
-		for loop {
-			select {
-			case err = <-cmdDone:
-				loop = false
-			case <-ctx.Done():
-				log.Printf("Execution of check '%s' was killed through context timeout.", checkID)
-				cmd.Process.Kill()
-				time.Sleep(100 * time.Millisecond)
-			}
-		}
-	}
-
-	success := err == nil
-
-	checkResultsLock.Lock()
-
-	if _, ok := checkResults[checkID]; !ok {
-		checkResults[checkID] = &checkResult{
-			Check: check,
-		}
-	}
-
-	if success == checkResults[checkID].IsSuccess {
-		checkResults[checkID].Streak++
-	} else {
-		checkResults[checkID].IsSuccess = success
-		checkResults[checkID].Streak = 1
-	}
-
-	if !success {
-		log.Printf("Check %q failed, streak now at %d, error was: %s", checkID, checkResults[checkID].Streak, err)
-	}
-
-	lastResultRegistered = time.Now()
-
-	checkResultsLock.Unlock()
-}
-
-func handleELBHealthCheck(res http.ResponseWriter, r *http.Request) {
-	healthy := true
-	start := time.Now()
-	buf := bytes.NewBuffer([]byte{})
+func handleELBHealthCheck(w http.ResponseWriter, _ *http.Request) {
+	var (
+		healthy = true
+		start   = time.Now()
+		buf     = new(bytes.Buffer)
+	)
 
 	checkResultsLock.RLock()
 	for _, cr := range checkResults {
@@ -214,13 +125,15 @@ func handleELBHealthCheck(res http.ResponseWriter, r *http.Request) {
 	}
 	checkResultsLock.RUnlock()
 
-	res.Header().Set("X-Collection-Parsed-In", strconv.FormatInt(time.Since(start).Nanoseconds()/int64(time.Microsecond), 10)+"ms")
-	res.Header().Set("X-Last-Result-Registered-At", lastResultRegistered.Format(time.RFC1123))
+	w.Header().Set("X-Collection-Parsed-In", strconv.FormatInt(time.Since(start).Nanoseconds()/int64(time.Microsecond), 10)+"ms")
+	w.Header().Set("X-Last-Result-Registered-At", lastResultRegistered.Format(time.RFC1123))
 	if healthy {
-		res.WriteHeader(http.StatusOK)
+		w.WriteHeader(http.StatusOK)
 	} else {
-		res.WriteHeader(http.StatusInternalServerError)
+		w.WriteHeader(http.StatusInternalServerError)
 	}
 
-	io.Copy(res, buf)
+	if _, err := io.Copy(w, buf); err != nil {
+		logrus.WithError(err).Error("writing HTTP response body")
+	}
 }

prefixed_logger.go

@@ -1,51 +0,0 @@
-package main
-
-import (
-	"bytes"
-	"fmt"
-	"io"
-	"sync"
-)
-
-type prefixedLogger struct {
-	channel       string
-	wrappedWriter io.Writer
-
-	buffer     []byte
-	bufferLock sync.Mutex
-}
-
-func newPrefixedLogger(wrappedWriter io.Writer, channel string) *prefixedLogger {
-	return &prefixedLogger{
-		channel:       channel,
-		wrappedWriter: wrappedWriter,
-		buffer:        []byte{},
-	}
-}
-
-func (p *prefixedLogger) dropCR(data []byte) []byte {
-	if len(data) > 0 && data[len(data)-1] == '\r' {
-		return data[0 : len(data)-1]
-	}
-	return data
-}
-
-func (p *prefixedLogger) Write(in []byte) (n int, err error) {
-	p.bufferLock.Lock()
-	defer p.bufferLock.Unlock()
-
-	n = len(in)
-	p.buffer = append(p.buffer, in...)
-
-	for {
-		if i := bytes.IndexByte(p.buffer, '\n'); i >= 0 {
-			// We have a full newline-terminated line.
-			fmt.Fprintf(p.wrappedWriter, "[%s] %s\n", p.channel, string(p.dropCR(p.buffer[0:i])))
-			p.buffer = p.buffer[i+1 : len(p.buffer)]
-		} else {
-			break
-		}
-	}
-
-	return
-}

prefixed_logger_test.go

@@ -1,34 +0,0 @@
-package main
-
-import (
-	"bytes"
-	"testing"
-)
-
-func TestPrefixedLogger(t *testing.T) {
-	var (
-		buf = bytes.NewBuffer([]byte{})
-		pl  = newPrefixedLogger(buf, "baum")
-		n   int
-		err error
-	)
-
-	n, err = pl.Write([]byte("non-newline terminated string"))
-	if n != 29 || err != nil {
-		t.Fatalf("Write to prefixedLogger had unexpected results: n=29 != %d, err=nil != %s", n, err)
-	}
-
-	if n = len(buf.Bytes()); n != 0 {
-		t.Fatalf("Buffer contains %d characters, should contain 0", n)
-	}
-
-	pl.Write([]byte("now a newline\nand something"))
-	if n = len(buf.Bytes()); n != 50 {
-		t.Fatalf("Buffer contains %d characters, should contain 50", n)
-	}
-
-	pl.Write([]byte(" more to log\nwith multiple\nnewlines\n"))
-	if n = len(buf.Bytes()); n != 120 {
-		t.Fatalf("Buffer contains %d characters, should contain 120", n)
-	}
-}