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Commit18973a6

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fix: Add reaper to coder agent (#2441)
* fix: Add reaper to coder agent- The coder agent runs as PID 1 in some of our Docker workspaces. In such cases it is the responsibility of the init process to reap dead processes. Failing to do so can result in an inability to create new processes by running out of PIDs. This PR adds a reaper to our agent that is only spawned if it detects that it is PID1.
1 parent6c1208e commit18973a6

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7 files changed

+191
-2
lines changed

7 files changed

+191
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lines changed

‎agent/reaper/doc.go

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// Package reaper contains logic for reaping subprocesses. It is
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// specifically used in the agent to avoid the accumulation of
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// zombie processes.
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package reaper

‎agent/reaper/reaper_stub.go

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//go:build !linux
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package reaper
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import"github.com/hashicorp/go-reap"
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// IsChild returns true if we're the forked process.
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funcIsChild()bool {
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returnfalse
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}
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// IsInitProcess returns true if the current process's PID is 1.
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funcIsInitProcess()bool {
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returnfalse
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}
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funcForkReap(pids reap.PidCh)error {
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returnnil
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}

‎agent/reaper/reaper_test.go

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//go:build linux
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package reaper_test
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import (
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"os"
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"os/exec"
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"testing"
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"time"
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"github.com/hashicorp/go-reap"
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"github.com/stretchr/testify/require"
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"github.com/coder/coder/agent/reaper"
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)
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funcTestReap(t*testing.T) {
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t.Parallel()
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// Don't run the reaper test in CI. It does weird
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// things like forkexecing which may have unintended
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// consequences in CI.
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if_,ok:=os.LookupEnv("CI");ok {
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t.Skip("Detected CI, skipping reaper tests")
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}
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// Because we're forkexecing these tests will try to run twice...
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ifreaper.IsChild() {
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t.Skip("I'm a child!")
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}
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// OK checks that's the reaper is successfully reaping
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// exited processes and passing the PIDs through the shared
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// channel.
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t.Run("OK",func(t*testing.T) {
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pids:=make(reap.PidCh,1)
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err:=reaper.ForkReap(pids)
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require.NoError(t,err)
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cmd:=exec.Command("tail","-f","/dev/null")
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err=cmd.Start()
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require.NoError(t,err)
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cmd2:=exec.Command("tail","-f","/dev/null")
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err=cmd2.Start()
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require.NoError(t,err)
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err=cmd.Process.Kill()
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require.NoError(t,err)
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err=cmd2.Process.Kill()
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require.NoError(t,err)
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expectedPIDs:= []int{cmd.Process.Pid,cmd2.Process.Pid}
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deadline:=time.NewTimer(time.Second*5)
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fori:=0;i<len(expectedPIDs);i++ {
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select {
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case<-deadline.C:
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t.Fatalf("Timed out waiting for process")
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casepid:=<-pids:
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require.Contains(t,expectedPIDs,pid)
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}
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}
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})
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}

‎agent/reaper/reaper_unix.go

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//go:build linux
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package reaper
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import (
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"fmt"
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"os"
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"syscall"
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"github.com/hashicorp/go-reap"
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"golang.org/x/xerrors"
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)
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// agentEnvMark is a simple environment variable that we use as a marker
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// to indicated that the process is a child as opposed to the reaper.
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// Since we are forkexec'ing we need to be able to differentiate between
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// the two to avoid fork bombing ourselves.
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constagentEnvMark="CODER_DO_NOT_REAP"
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// IsChild returns true if we're the forked process.
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funcIsChild()bool {
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returnos.Getenv(agentEnvMark)!=""
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}
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// IsInitProcess returns true if the current process's PID is 1.
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funcIsInitProcess()bool {
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returnos.Getpid()==1
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}
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// ForkReap spawns a goroutine that reaps children. In order to avoid
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// complications with spawning `exec.Commands` in the same process that
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// is reaping, we forkexec a child process. This prevents a race between
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// the reaper and an exec.Command waiting for its process to complete.
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// The provided 'pids' channel may be nil if the caller does not care about the
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// reaped children PIDs.
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funcForkReap(pids reap.PidCh)error {
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// Check if the process is the parent or the child.
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// If it's the child we want to skip attempting to reap.
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ifIsChild() {
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returnnil
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}
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goreap.ReapChildren(pids,nil,nil,nil)
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args:=os.Args
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// This is simply done to help identify the real agent process
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// when viewing in something like 'ps'.
48+
args=append(args,"#Agent")
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pwd,err:=os.Getwd()
51+
iferr!=nil {
52+
returnxerrors.Errorf("get wd: %w",err)
53+
}
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55+
pattrs:=&syscall.ProcAttr{
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Dir:pwd,
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// Add our marker for identifying the child process.
58+
Env:append(os.Environ(),fmt.Sprintf("%s=true",agentEnvMark)),
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Sys:&syscall.SysProcAttr{
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Setsid:true,
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},
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Files: []uintptr{
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uintptr(syscall.Stdin),
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uintptr(syscall.Stdout),
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uintptr(syscall.Stderr),
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},
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}
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//#nosec G204
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pid,_:=syscall.ForkExec(args[0],args,pattrs)
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varwstatus syscall.WaitStatus
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_,err=syscall.Wait4(pid,&wstatus,0,nil)
74+
forxerrors.Is(err,syscall.EINTR) {
75+
_,err=syscall.Wait4(pid,&wstatus,0,nil)
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}
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returnnil
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}

‎cli/agent.go

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"net/url"
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"os"
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"path/filepath"
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"runtime"
1112
"time"
1213

1314
"cloud.google.com/go/compute/metadata"
@@ -18,6 +19,7 @@ import (
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"cdr.dev/slog/sloggers/sloghuman"
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2021
"github.com/coder/coder/agent"
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"github.com/coder/coder/agent/reaper"
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"github.com/coder/coder/cli/cliflag"
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"github.com/coder/coder/codersdk"
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"github.com/coder/retry"
@@ -51,6 +53,23 @@ func workspaceAgent() *cobra.Command {
5153
}
5254
deferlogWriter.Close()
5355
logger:=slog.Make(sloghuman.Sink(cmd.ErrOrStderr()),sloghuman.Sink(logWriter)).Leveled(slog.LevelDebug)
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57+
isLinux:=runtime.GOOS=="linux"
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59+
// Spawn a reaper so that we don't accumulate a ton
60+
// of zombie processes.
61+
ifreaper.IsInitProcess()&&!reaper.IsChild()&&isLinux {
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logger.Info(cmd.Context(),"spawning reaper process")
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err:=reaper.ForkReap(nil)
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iferr!=nil {
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logger.Error(cmd.Context(),"failed to reap",slog.Error(err))
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returnxerrors.Errorf("fork reap: %w",err)
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}
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logger.Info(cmd.Context(),"reaper process exiting")
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returnnil
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}
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client:=codersdk.New(coderURL)
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ifpprofEnabled {

‎go.mod

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github.com/golang-migrate/migrate/v4v4.15.2
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github.com/google/go-github/v43v43.0.1-0.20220414155304-00e42332e405
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github.com/google/uuidv1.3.0
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github.com/hashicorp/go-reapv0.0.0-20170704170343-bf58d8a43e7b
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github.com/hashicorp/go-versionv1.5.0
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github.com/hashicorp/hc-installv0.3.2
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github.com/hashicorp/hcl/v2v2.12.0
@@ -131,8 +132,6 @@ require (
131132
storj.io/drpcv0.0.30
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)
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134-
requiregithub.com/xi2/xzv0.0.0-20171230120015-48954b6210f8// indirect
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require (
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github.com/agnivade/levenshteinv1.0.1// indirect
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github.com/elastic/go-windowsv1.0.0// indirect
@@ -240,6 +239,7 @@ require (
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github.com/xeipuuv/gojsonpointerv0.0.0-20190905194746-02993c407bfb// indirect
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github.com/xeipuuv/gojsonreferencev0.0.0-20180127040603-bd5ef7bd5415// indirect
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github.com/xeipuuv/gojsonschemav1.2.0// indirect
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github.com/xi2/xzv0.0.0-20171230120015-48954b6210f8// indirect
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github.com/yashtewari/glob-intersectionv0.1.0// indirect
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github.com/zclconf/go-ctyv1.10.0// indirect
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github.com/zeebo/errsv1.2.2// indirect

‎go.sum

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@@ -896,6 +896,8 @@ github.com/hashicorp/go-multierror v1.0.0/go.mod h1:dHtQlpGsu+cZNNAkkCN/P3hoUDHh
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github.com/hashicorp/go-multierrorv1.1.0/go.mod h1:spPvp8C1qA32ftKqdAHm4hHTbPw+vmowP0z+KUhOZdA=
897897
github.com/hashicorp/go-multierrorv1.1.1 h1:H5DkEtf6CXdFp0N0Em5UCwQpXMWke8IA0+lD48awMYo=
898898
github.com/hashicorp/go-multierrorv1.1.1/go.mod h1:iw975J/qwKPdAO1clOe2L8331t/9/fmwbPZ6JB6eMoM=
899+
github.com/hashicorp/go-reapv0.0.0-20170704170343-bf58d8a43e7b h1:3GrpnZQBxcMj1gCXQLelfjCT1D5MPGTuGMKHVzSIH6A=
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github.com/hashicorp/go-reapv0.0.0-20170704170343-bf58d8a43e7b/go.mod h1:qIFzeFcJU3OIFk/7JreWXcUjFmcCaeHTH9KoNyHYVCs=
899901
github.com/hashicorp/go-rootcertsv1.0.0/go.mod h1:K6zTfqpRlCUIjkwsN4Z+hiSfzSTQa6eBIzfwKfwNnHU=
900902
github.com/hashicorp/go-sockaddrv1.0.0/go.mod h1:7Xibr9yA9JjQq1JpNB2Vw7kxv8xerXegt+ozgdvDeDU=
901903
github.com/hashicorp/go-syslogv1.0.0/go.mod h1:qPfqrKkXGihmCqbJM2mZgkZGvKG1dFdvsLplgctolz4=

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